Postgresql unique index multiple columns. So, I created a "stockmodel.

If those columns are numeric or float (rather than integer or bigint) using '-Infinity' might be a better substitution value. Also, updates on a row that is not included in a conditional index do not have to spend time updating the index. (At present, only b-tree supports it. You can create indices for any columns of your entity. You might want to adjust this to allow users to confirm multiple addresses, but have a single "primary" address. The basic syntax is: CREATE INDEX index_name ON table_name (column_name); For example, if we have a table users with a column email, we can create an index like this: CREATE Sep 11, 2022 · Postgres enables us to implement the UNIQUE constraint on more than one column using the following syntax: CREATE TABLE tab_name ( col_1 data_type, col_2 data_type, …, col_n data_type, UNIQUE (col_1, col_2)); The following syntax will work the same way as the above syntax: CREATE TABLE tab_name(. I want my unique index to allow empty values. You must need to define a unique index on those columns which you are planning to use in ON CONFLICT clause because it can only check the duplicates bases on unique indexes only. Also, we can define the UNIQUE INDEX on multiple columns to enforce them to store the combined unique value. . In this comprehensive guide, we will explore the PostgreSQL UNIQUE constraint across multiple table columns. An access method that supports this feature sets amcanunique true. Example 1: 171. Also, I am having trouble understanding why one would generate multiple indexes on a single table: ADD PRIMARY KEY (table_id), ADD UNIQUE INDEX idx_table_table_id (table_id), ADD INDEX idx_table_code (table_code), The last insert fails because it violates the unique index on column foo when it tries to insert the value 1 into this column for a second time. In MySQL you can use SHOW INDEXES FOR table and look at the Column_name column. An operator class with optional parameters can be specified for each Feb 17, 2024 · This is where multi-column unique indexes come into play. Jun 24, 2019 · You need to use pg_index and limit to those that have indisunique. The unique When an index is declared unique, multiple table rows with equal indexed values are not allowed. PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a May 11, 2024 · A unique constraint can be either a column constraint or a table constraint. i prefer to make EmpID as PK (from the current design, its a manual input, not an auto increment ID) and in case resigned employee join the company again then they will get new Apr 27, 2016 · INSERT INTO mytable(col1, col2, col3) VALUES ('A', 'B', 0) ON CONFLICT (col1, col2) DO UPDATE SET col3 = EXCLUDED. This will be your complete DDL for rejecting multiple null; This will be your complete DDL: CREATE TABLE tbl ( a_id integer NOT NULL, b_id integer NULL ); alter table tbl add constraint tbl_unique unique(a_id, b_id); create unique index tbl_unique_a_id on tbl(a_id) where b_id is null; Jan 6, 2024 · Before diving into multiple columns, let’s grasp the basic concept of the SELECT DISTINCT command. An operator class with optional parameters can be specified for each For a value index, the key fields for the index are specified as column names; multiple columns can be specified if the index access method supports multi-column indexes. However they Jun 18, 2024 · Defining Foreign Keys ¶. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the Mar 12, 2015 · I want to split one column that is colb in the given below example into two columns like column1 and column2. Also google I would like to get the columns that an index is on in PostgreSQL. Create a unique index with the CREATE UNIQUE INDEX command. Since the csv can be re-uploaded with some changes and I don't want the re-upload to create duplicates on rows that didn't change, I added a constraint and unique index with majority of the columns included in them. g. For a table like: CREATE TABLE data ( id SERIAL , day DATE , val NUMERIC ); CREATE INDEX data_day_val_idx ON data (day, val); I'd like to be able to [quickly] query only the distinct days. 5 and Section 11. You can create a database index for a specific column by using @Index on a column you want to make an index. So that these two rows are NOT allowed: 1,2,NULL 1,2,NULL Doing simple experiments at psql, this is exactly the behavior I see. Example: import { Entity, PrimaryGeneratedColumn, Column, Index } from "typeorm" @Entity() export class User { @PrimaryGeneratedColumn() id: number @Index() @Column() firstName Jul 12, 2024 · In this case, you can use index tag composite, it means the id of the composite index. Jan 7, 2021 · 2. nspname as table_schema from pg_index pgi join pg_class idx on idx. A multicolumn unique index will only reject cases where all indexed columns are equal in multiple rows. *,0)); This normally works, too: CREATE UNIQUE INDEX tbl_row_uni ON tbl (hash_record_extended(tbl,0)); But the first variant is safer. In a table, a column may contain duplicate values; and sometimes, you only want to list the different (unique) values. If you want to find distinct values of all columns in a table, you can use SELECT DISTINCT *: SELECT DISTINCT *. ) Columns listed in the INCLUDE clause are not considered when enforcing Aug 27, 2018 · SET enable_seqscan = OFF; Then: EXPLAIN. Let’s assume that multiple users of the library can have identical last names. PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a May 7, 2018 · @LaurenzAlbe havent try it myself but i guess you are right, maybe before insert trigger can be used for this scenario if OP want to do database level checking, otherwise application level checking will do the job. But not the other three unique constraints / indexes. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the Sep 19, 2013 · The second approach to create Unique Constraints with EF Core by using Alternate Keys. This is the easiest, most hassle-free approach. Whether there can be multiple key columns is independent of whether INCLUDE columns can be added to the Sep 25, 2021 · Generate hash id for records in DB. This value is only used for unique indexes. Oct 19, 2018 · It seems that there is no analog in postgres for generating multiple indexes on a single table. SELECT * FROM tbl ORDER BY ORDER BY x, y DESC; Now, if the index could be used in any way, it would be. relname as index_name, insp. Whether there can be multiple key columns is independent of whether INCLUDE columns can be added to the index. Depending on the percentage of matching rows, this may save a bit of storage space, or a lot relative to a full index. In PostgreSQL, the UNIQUE index to ensure the uniqueness of values in one or more columns. Also speeds up queries with conditions on one or both column. . To get the actual index and table names, you need to join that table to pg_class and pg_namespace: select idx. This is effectively pretty much the same as a unique constraint, because such constraints are implemented May 31, 2020 · An e-mail address can only be confirmed for one user: Unique Index On user_emails ( email ) Where is_confirmed Is True; Each user can have only one confirmed address: Unique Index On user_emails ( user_id ) Where is_confirmed Is True;. mysql> show indexes from foos; +-----+-- Oct 16, 2009 · This index should be non-unique - in mysql it should be something like: create index ndx_1 on model_quotemodel(sequence,stock); The only Django workaround I know of is creating an "sql" file that will be executed by django upon table creation. UNIQUE USING INDEX u_test_1; -- the above runs no problem. 11. col3 + 1; ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification. CREATE INDEX constructs an index on the specified column (s) of the specified relation, which can be a table or a materialized view. Uniqueness. relname as table_name, tnsp. 8. To solve our issue with unique names in the school class we will use the @Index decorator (that is then transformed to the INDEX in SQL). If false, this unique index will consider null values distinct (so the index can contain multiple null values in a column, the default PostgreSQL behavior). Indexes are primarily used to enhance database performance (though inappropriate use can result in slower performance). schoolClass which is a ManyToOne relation with Class table; name which is just a name of the student. CREATE UNIQUE INDEX idx ON tbl (columns); has a significant algorithmic performance benefit in PostgreSQL or MySQL implementations when scanning the indexed column(s), or whether the UNIQUE keyword simply introduces a unique constraint alongside the index. PostgreSQL uses unique indexes to implement unique constraints, so the effect is the same, with an important caveat: you can't perform upserts ( ON CONFLICT DO UPDATE) against a unique index like you would against a Jan 30, 2020 · 4. Aug 28, 2020 · Last Updated : 28 Aug, 2020. There is a drawback to this though: Whether there can be multiple key columns is independent of whether INCLUDE columns can be added to the index. This way, a unique index will be created behind the scenes, and you will get the behavior you need. May 11, 2023 · The PostgreSQL UNIQUE INDEX is used when we want to ensure that the column stores unique values only. cola, row2. The index covers the columns that make up the primary key or unique constraint (a Nov 23, 2014 · Use a view to do the distinct and then join it to the original table to pick one row of column C. pg_index #. The CHECK constraint is used to limit the value range that can be placed in a column. You have a few options: If at all possible, partition your tables so that the key ranges are exclusive in some way. For instance, assuming you wanted to query using test1 and test2, rank the results, and then retrieve the top 10 matches, you could use this query: ts_rank(. For example: Apr 14, 2013 · I have a multi-column unique index in postgresql. Jan 3, 2020 · This unique index will only contain rows satisfying the specified WHERE condition. PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a CREATE UNIQUE INDEX line_items_prod_var_null_idx ON line_items (product_id) WHERE variant_id IS NULL; This way you can enter (1,2), (1,3) and (1, null), but neither of them a second time. e. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the Jan 4, 2024 · Creating a Basic Index. Sometimes, you may want to add a unique constraint to an existing column or group of columns. Index Uniqueness Checks. You can see that in this index, the ordering via status is not present at all. They allow you to define a unique constraint on a group of columns, ensuring that the combined values are unique across all rows in the table. colb] This index could do the job (currently only gist indexes support Nov 2, 2015 · 454. Feb 8, 2022 · How to create a unique index for multiple columns. oid = pgi. It works similarly to the single-column index; the only difference is that we need a combination of columns to maintain uniqueness. We want make queries like: "items for account 1 with keyword k1". Design your indexes to match. The catalog pg_index contains part of the information about indexes. PostgreSQL doesn't define a partial (i. At the table level, we can define unique constraints across multiple columns. 11 for some discussion of the merits of different index I would like to set up a table in PostgreSQL such that two columns together must be unique. – Apr 20, 2021 · 2. CREATE TABLE camembert ( handle int , id int , num text , PRIMARY KEY (handle, id, num) ); In the case of a UNIQUE constraint, you probably also want all three columns to be marked NOT NULL. Feb 9, 2018 · 4. How can I do that? Current code for my postgres model: my_field string `gorm:"uniqueIndex"` Sep 28, 2021 · Again, postgresql can random-access the index to the first eligible row, then scan the index sequentially until it gets to the last eligible row. PostgreSQL enforces SQL uniqueness constraints using unique indexes, which are indexes that disallow multiple entries with identical keys. Index on Expression – Guide you on creating an index based on expressions. It is possible to create a unique PostgreSQL index for multiple columns. This query requires a composite GIN index on account_id and keywords column. A uniqueness restriction covering only some rows cannot be written as a unique constraint, but it is possible to enforce such a restriction by creating a unique partial index. So just: CREATE UNIQUE INDEX tbl_row_uni ON tbl (hash_record_extended(tbl. For example, for a hypertable named hypertable_example, partitioned on time and device_id, create an index on time and device_id: CREATEUNIQUEINDEX idx_deviceid_time. Constraints are one powerful mechanism for ensuring data accuracy. Note that PostgreSQL also offers the DISTINCT ON clause that retains the first unique entry of a column or combination of columns in the result set. When I add an unique constraint: ALTER TABLE assignment ADD CONSTRAINT unique_assignment UNIQUE (dining_table_id, guest_group_id, start_timestamp, end_timestamp); I get: A multicolumn unique index will only reject cases where all indexed columns are equal in multiple rows. colA colB. use a UNIQUE constraint instead of a PRIMARY KEY constraint if you want to enforce the uniqueness of a column, or combination of columns, that is not the primary key. That's not what the multicolumn UNIQUE index achieves. conditional) UNIQUE constraint - however, you can create a partial unique index. Mar 18, 2021 · 3. ADD CONSTRAINT unique_target_1. Let’s take a look at the following example. Primary key versus unique index. But you'll still see a sequential scan. Short syntax with "column constraints": sl_no int PRIMARY KEY -- NOT NULL due to PK. Plus, that information can be picked up by information_schema to do some metadata inferring if necessary on the fact that both need to be unique. Null values are not considered equal. Multicolumn Indexes – Show you how to define indexes that include multiple table columns. You‘ll learn the syntax, use cases, limitations, and best practices for leveraging UNIQUE constraints in May 11, 2015 · ); create unique index example_index on example ( field1 asc, field2 asc, field3 asc, field4 asc, field5 asc ); On both Oracle and SQL Server, leaving any of the nullable columns NULL will result in only performing a uniqueness check on the non-null columns. It will create only one index on two columns and both the column combinedly can not contain duplicate in the entire table. To specify multiple columns in the constraint/index or to specify an explicit name, use the UniqueConstraint or Index Sep 1, 2021 · I have a string column inside my Postgres DB, which has a unique index, but I want to allow duplicate values in some rows when the column is empty. person_to_person_composite_crosstable (id, combined_id); If used, the above index should let the join happen faster. Sometimes one of these column values will be NULL, and I'd like the unique index to treat NULL as just another value. See also Section 11. cola, row1. 53. then it might be appropriate to define an index on the columns major and minor together, e. Is there a solution which works also with PostgreSQL (Npgsql provider) ? Dec 4, 2020 · While Postgres doesn't allow a partially unique constraint, it does support a partial unique index: create unique index unique_row on myTable(content_id, brand_id) where not is_archived; See Partial Indexes in the Postgres documentation. The constraint will use btree operators <> and =, hence you have to install btree_gist extension. The rest is mostly in pg_class. In table description (\d in psql) you can tell unique constraint from unique index. Aug 31, 2020 · The solution of Does EF Core allow a unique column to contain multiple nulls? works perfect with Microsoft SQL Server but not with PostgreSQL. your database requirements for primary keys and other constraints. PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a table. A foreign key in SQL is a table-level construct that constrains one or more columns in that table to only allow values that are present in a different set of columns, typically but not always located on a different table. Relational database management systems like PostgreSQL provide various techniques for enforcing data integrity. PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a Mar 9, 2016 · When performing inference, it consists of one or more index_column_name columns and/or index_expression expressions, and an optional index_predicate. This is a single-column index (namely, the Aug 4, 2022 · Our Table has three columns: id which is a unique ID for the certain record. This only seems to work in instances where the second column is a boolean type. When an index is declared unique, multiple table rows with equal indexed values are not allowed. Apr 24, 2020 · A multicolumn index will index rows by id, then rows ordered by id's are further indexes by status and then with result and so on. The value of the column c2 or c3 needs not to be unique. CREATE UNIQUE INDEX CONCURRENTLY u_test_2 ON unique_test (unique_no); ALTER TABLE unique_test. You can add multiple duplicates for colA but considering that the colB is different for each row having same colA and vice-versa. Below is a demonstration of this: Create a table with sample data with composite PRIMARY KEY: 1. The PostgreSQL unique index enforces the uniqueness of values in one or multiple columns. The question is a bit unclear about whether you want multiple indexes or a single index on multiple columns (and was more confused before I edited it - originally it delightfully asked for "an index that contain multiple multiple index"). create extension if not exists btree_gist; create table my_table(. In Postgres, the to_tsvector function only accepts a single column as input. You can do what you are already thinking of: create a unique constraint on both fields. For instance: id int PRIMARY KEY AUTOINCREMENT, col1 int NOT NULL, col2 int NOT NULL. ) Only B-tree currently supports unique indexes. The optional INCLUDE clause adds to that index one or more columns that are simply “ payload ”: uniqueness is not enforced on them, and the index cannot be searched on the basis of those columns. col1 int, col2 text, exclude using gist (col1 with <>, col2 with =) ); Jan 20, 2015 · And I created an unique_index on the uid column inside the offers table: ALTER TABLE offers ADD CONSTRAINT offer_unique_index UNIQUE(uid); So everytime the postgresql function gets the same price and valid values, it will try to insert the same md5 hash and so will violate the unique constraint. Jan 14, 2021 · I created a table in postgres that includes various columns that based on an import from a csv. It is only available on rows indexed by the id's first. This is a typical case for using an exclude constraint. Partial index – Learn about creating partial indexes that include a subset of rows of the indexed columns. name TEXT NOT NULL, value TEXT NOT NULL, PRIMARY KEY (name, value) ); I frequently do a query to see what value s are available: SELECT DISTINCT value FROM items; By default, when you create a unique index, PostgreSQL treats null values as distinct; this means that a unique index can contain multiple null values in a column. nspname as index_schema, tbl. create table t3 ( cola varchar, colb varchar ); Dec 12, 2022 · I already use a trigger to check the uniqueness, but it creates problems for multi-threaded row recording because when two transactions write two identical rows simultaneously, the trigger performs a uniqueness check for transactions and since the trigger works BEFORE applying the transaction, there are no conflicting records in the database at the time of checking, the check is successful and Dec 6, 2019 · create unique index on the_table (coalesce(a,-1), coalesce(b, -1), coalesce(c, -1)); That way NULL values are treated the same inside the index, without the need to use them in the table. PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a Unique constraint is used to enforce data integrity in PostgreSQL tables. But this does not mean that we cannot do a full text search using multiple columns. -- check what happens when column is not unique. That makes the expression index much more attractive than a generated column plus index. Adding unique constraints using a unique index. The index covers the columns that make up the primary key or unique constraint (a Dec 19, 2017 · BTW: The purpose of the least and greatest functions is so that when one ID is in red, it can't also be in another record in the blue column. Creating a unique index on multiple columns in PostgreSQL is a simple yet powerful operation. Only the combination is unique, so (1,3) would be a dupe of (3,1), but (2,1) is still allowed, so 1 can still be in another record in the blue column. Inserting into the target is left for you to figure out. You can't have a partial unique constraint, but you can create a partial unique index, which implements the very same functionality: Demo on DB FIddle: -- DETAIL: Key (number)=(123) already exists. Corner case exception: If an index-only scan is possible, the index might still be used if it's substantially smaller than the table. colb] && ARRAY[row2. : CREATE INDEX test2_mm_idx ON test2 (major, minor); Currently, only the B-tree, GiST, GIN, and BRIN index types support multiple-key-column indexes. Unique indexes address the partition, not the table as a whole. When creating an index, you can also instruct PostgreSQL that nulls should be treated as non-distinct ; this causes a unique constraint violation to be raised if a column contains Multicolumn indexes should be used sparingly. A single index scan can only use query clauses that use the index's columns with operators of its operator class and are joined with AND. Combining Multiple Indexes #. To create an index in PostgreSQL, you can use the CREATE INDEX command followed by the name of the index and the table column you wish to index. Mar 20, 2015 · Not sure if this is possible in PostgreSQL 9. There can only be one PRIMARY KEY constraint per table (spanning one or more columns) - as indicated by the word "primary". Jun 11, 2015 · Unique constraints are just specific exclusion constraints (they are based on equality collisions ). Note that I cover the combined_id column, which is required by the select. Make sure to include all partitioning columns in the index. An operator class with optional parameters can be specified for each For more info, see the Postgres doc for Constraints, the "Unique Constraints" section. JPA allows us to define unique constraints in our code using @Column (unique=true) and @UniqueConstraint. You need a multicolumnUNIQUE or PRIMARY KEY constraint. Put the equality-match columns first in the index, then the range match (COL_TIME >= ?) column. Jan 21, 2016 · I am curious as to whether . So, in theory, you just need to exclude every row1, where there is already a row2, for which this expression is true: ARRAY[row1. 61. I have a PostgreSQL table that looks like this: CREATE TABLE items (. If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row. The index covers the columns that make up the primary key or unique constraint (a Apr 17, 2017 · The answer is: Yes. test=# insert into master values (0, 0); INSERT 0 1. In MySQL a unique constraint allows multiple NULLs. We call the columns which are constrained the foreign key columns and the columns which they are When an index is declared unique, multiple table rows with equal indexed values are not allowed. ON table_name(column_name, []); Note: O nly B-tree indexes can be declared as unique indexes. All table_name unique indexes that, without regard to order, contain exactly the conflict_target-specified columns/expressions are inferred (chosen) as arbiter indexes. The key field (s) for the index are specified as column names, or alternatively Jul 28, 2021 · As for performance, the following index on the crosstable might speed up the query: CREATE INDEX idx ON people. One column: Multiple columns: EF 6 and below: First approach: @"CREATE UNIQUE INDEX LX_{0} ON {0} ({1})", "Entitys", "FirstColumn, SecondColumn")); This approach is very fast and useful but the main problem is that Entity Framework doesn't know 338. You can have additional UNIQUE constraints (spanning one or more columns). Or use the NULLS NOT DISTINCT clause in Postgres 15 or later. Apr 18, 2023 · Another solution that support multiple columns index, based on @Kragh answer. In most situations, an index on a single column is sufficient and saves space and time. Actually, we need an inverted index, with rows like this: (the key for each row should be composite) (account_id, keyword) --> [item1, item2, ] What's the right way to create this index in postgresql? 5. To alter an existing table use the ALTER TABLE syntax you already tried. For a functional index, an index is defined on the result of a function applied to one or more attributes of a single class. Do have the look at video, it explains all this pretty well. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the Null values are not considered equal. 26. It ensures that no duplicate values are entered in specific columns that is not primary key column. FROM table_name; The star or asterisk ( *) means all columns of the table_name. CREATE INDEX idx ON tbl (columns); vs. Indexes with more than three columns are unlikely to be helpful unless the usage of the table is extremely stylized. oid = idx May 6, 2012 · INDEX and UNIQUE INDEX can. This syntax seems to be designed for a single composite unique constraint over two columns, rather than two constraints. Let's check uniqueness, just in case. To quote: If a unique constraint refers to a group of columns, the columns are listed separated by commas… This specifies that the combination of values in the indicated columns is unique across the whole table, though any one of the columns need not be When an index is declared unique, multiple table rows with equal indexed values are not allowed. Creating a Unique Index on Multiple Columns. In other words, partition on key data. May 28, 2012 · 3. (This limit can be altered when building PostgreSQL. If we define the UNIQUE INDEX on the particular column, then that column can not have the same value in multiple rows. Extract from the documentation of the Column: unique – When True, indicates that this column contains a unique constraint, or if index is True as well, indicates that the Index should be created with the unique flag. To create a UNIQUE index, you can use the following syntax: Syntax: CREATE UNIQUE INDEX index_name. All fields which have the same composite id of the struct are put together to the same index, just like the original rule. Examples. So, col1 and col2 can repeat, but not at the same time. See: Create unique constraint with The combination of values in the columns c2 and c3 will be unique across the whole table. 5. You can include other columns as well if needed. sql" containing the following query (same as above:) Adding a unique constraint will automatically create a unique btree index on the column or group of columns used in the constraint. In your case, ON CONFLICT (id, core_id) determines (only!) the multicolumn unique constraint id_core_id_unique. So, I created a "stockmodel. CREATE or replace FUNCTION create_index(_index text, _table text, VARIA DIC param_args text[]) RETURNS void AS $$ declare l_count integer; begin select count(*) into l_count from pg_indexes where schemaname = 'public' and tablename = lower(_table) and indexname = lower(_index); if l_count = 0 then EXECUTE format Feb 10, 2024 · All table_name unique indexes that, without regard to order, contain exactly the conflict_target-specified columns/expressions are inferred (chosen) as arbiter indexes. There can be multiple values of either value, so long as there are not two that share both. 3+, but I'd like to create a unique index on a non-unique column. indexrelid join pg_namespace insp on insp. Things that are the same: A primary key implies a unique Adding a unique constraint will automatically create a unique B-tree index on the column or group of columns listed in the constraint. Indexes can have up to 32 columns, including INCLUDE columns. The DISTINCT clause in PostgreSQL is used to return only distinct (different) values. This is the current behavior of PostgreSQL. But no matter, I guess, since zzzeek's answer addresses both cases. Oh, and you could pick up multiple columns from t, not just c - the only thing is that your subquery needs to find a way to limit it to only one row. Unique Index – Provide you with steps for defining unique indexes. Description. I have a table with two columns: Example:. It is possible to make a unique index on mutiple columns. If you define a CHECK constraint on a column it will allow only certain values for this column. To create a unique index, you use the following CREATE UNIQUE INDEX statement: ON table_name ( column [, ]) In this syntax: First, specify the index name in the CREATE UNIQUE INDEX statement. But the improvement is it lets the most derived/embedding struct generates the name of index by NamingStrategy. Further reading. Aug 12, 2020 · CREATE UNIQUE INDEX CONCURRENTLY u_test_1 ON unique_test (unique_yes); ALTER TABLE unique_test. Tejash SO. For example, given an index on (a, b) a query condition like WHERE a = 5 AND b = 6 could use the index, but a query like WHERE a = 5 OR b = 6 could not directly use the index. test=# insert into master values (0, 1); ERROR: duplicate key value violates unique constraint "master_con_id_key". wf sw vz kx yg pd eb bi ig yf