Query
SQL SELECT
Query rows from one or more tables.
SELECT [DISTINCT] column_list FROM table_name [WHERE condition] [GROUP BY columns] [HAVING condition] [ORDER BY columns] [LIMIT count];Open guide SQL reference
Common SQL statements and patterns, with notes for six database dialects.
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56 entries
Data changes
SQL INSERT
Add rows to a table.
INSERT INTO table_name (column_a, column_b) VALUES (value_a, value_b);Open guide Data changes
SQL UPDATE
Change values in existing rows.
UPDATE table_name SET column = value [, column = value] WHERE condition;Open guide Data changes
SQL DELETE
Remove matching rows from a table.
DELETE FROM table_name WHERE condition;Open guide Data changes
SQL MERGE / UPSERT
Insert or update rows according to a match condition; syntax differs by database.
MERGE INTO target USING source ON match_condition WHEN MATCHED THEN UPDATE SET ... WHEN NOT MATCHED THEN INSERT ...;Open guide Schema
SQL CREATE TABLE
Create a table with columns and constraints.
CREATE TABLE table_name (column_name data_type [constraint], ...);Open guide Schema
SQL ALTER TABLE
Change a table definition; supported operations vary by dialect.
ALTER TABLE table_name ADD COLUMN column_name data_type;Open guide Schema
SQL DROP TABLE
Remove a table definition and its data.
DROP TABLE [IF EXISTS] table_name;Open guide Schema
SQL TRUNCATE TABLE
Remove all rows efficiently where supported; transaction and identity behaviour varies.
TRUNCATE TABLE table_name;Open guide Schema
SQL CREATE INDEX
Create an index to support selected query patterns.
CREATE [UNIQUE] INDEX index_name ON table_name (column_list);Open guide Schema
SQL CREATE VIEW
Create a named query that can be referenced like a table.
CREATE VIEW view_name AS SELECT ...;Open guide Schema
SQL CREATE DATABASE
Create a database where supported by the engine and current connection context.
CREATE DATABASE database_name;Open guide Query
SQL JOIN
Combine rows from related tables using a join condition.
SELECT columns FROM left_table [INNER|LEFT|RIGHT|FULL] JOIN right_table ON condition;Open guide Query
SQL UNION / UNION ALL
Combine compatible result sets; UNION removes duplicates while UNION ALL keeps them.
query_1 UNION [ALL] query_2;Open guide Query
SQL WITH (CTE)
Define a common table expression for a single statement.
WITH cte_name AS (SELECT ...) SELECT ... FROM cte_name;Open guide Query
SQL Window functions
Calculate values across related rows without collapsing the result set.
function(...) OVER (PARTITION BY ... ORDER BY ...);Open guide Query
SQL CASE
Return a value based on conditional branches.
CASE WHEN condition THEN value [ELSE value] ENDOpen guide Access control
SQL GRANT
Grant privileges to a database principal; privilege names and scope vary by engine.
GRANT privilege ON object TO principal;Open guide Access control
SQL REVOKE
Remove previously granted privileges where supported.
REVOKE privilege ON object FROM principal;Open guide Transactions
SQL BEGIN / START TRANSACTION
Begin an explicit transaction; exact keywords vary by database.
BEGIN [TRANSACTION];Open guide Transactions
SQL COMMIT
Make the current transaction's changes permanent.
COMMIT [TRANSACTION];Open guide Transactions
SQL ROLLBACK
Undo uncommitted changes in the current transaction where supported.
ROLLBACK [TRANSACTION];Open guide Transactions
SQL SAVEPOINT
Mark a point within a transaction to which work can be rolled back.
SAVEPOINT savepoint_name;Open guide Administration
SQL EXPLAIN
Show a query execution plan; output and options differ by engine.
EXPLAIN [options] query;Open guide Access control
SQL CREATE USER
Create a database principal; authentication syntax is vendor-specific.
CREATE USER user_name ...;Open guide Access control
SQL GRANT ROLE
Assign a role to a principal using database-specific syntax.
GRANT role_name TO principal;Open guide Administration
SQL Inspect tables and schemas
Inspect schema metadata; these commands are client-specific rather than portable SQL.
Use the database client's schema inspection command or query its information schema/catalog.Open guide Query
SQL DISTINCT
Remove duplicate rows from a result set.
SELECT DISTINCT column FROM table;Open guide Query
SQL WHERE
Filter rows using a condition.
SELECT ... FROM table WHERE condition;Open guide Query
SQL GROUP BY
Group rows for aggregate calculations.
SELECT expression, aggregate(...) FROM table GROUP BY expression;Open guide Query
SQL HAVING
Filter grouped results after aggregation.
SELECT ... GROUP BY ... HAVING condition;Open guide Query
SQL ORDER BY
Sort query results by one or more expressions.
SELECT ... ORDER BY expression [ASC|DESC];Open guide Query
SQL LIMIT / OFFSET / FETCH
Limit or skip rows; the syntax differs across database dialects.
SELECT ... ORDER BY ... LIMIT count OFFSET offset;Open guide Query
SQL Subqueries
Use a query as an expression, source or predicate inside another statement.
SELECT ... WHERE value IN (SELECT ...);Open guide Schema
SQL Constraints
Enforce data rules using NOT NULL, UNIQUE, CHECK, PRIMARY KEY and FOREIGN KEY constraints.
CREATE TABLE ... (column type NOT NULL, UNIQUE (...), CHECK (...), FOREIGN KEY (...) REFERENCES ...);Open guide Schema
SQL PRIMARY KEY
Identify rows uniquely and enforce non-null uniqueness.
PRIMARY KEY (column_list)Open guide Schema
SQL FOREIGN KEY
Enforce references between related tables when enabled and supported.
FOREIGN KEY (column) REFERENCES parent_table (column)Open guide Administration
SQL CREATE SCHEMA
Create a namespace where supported; schema semantics vary by database.
CREATE SCHEMA schema_name;Open guide Schema
SQL ALTER / DROP INDEX
Change or remove an index using engine-specific syntax.
DROP INDEX index_name; -- ALTER syntax varies by engineOpen guide Schema
SQL DROP VIEW
Remove a view definition.
DROP VIEW [IF EXISTS] view_name;Open guide Schema
SQL DROP DATABASE
Remove a database where supported; this is destructive and often irreversible.
DROP DATABASE database_name;Open guide Transactions
SQL ROLLBACK TO SAVEPOINT
Undo a portion of a transaction to a savepoint where supported.
ROLLBACK TO SAVEPOINT savepoint_name;Open guide Access control
SQL GRANT / REVOKE
Manage database privileges; object scope, roles and syntax differ across engines.
GRANT privilege ON object TO principal;
REVOKE privilege ON object FROM principal;Open guide Query
SQL COALESCE / NULL handling
Return the first non-NULL value; NULL comparison rules require IS NULL / IS NOT NULL.
COALESCE(expression, fallback)Open guide Query
SQL Date and time functions
Work with date/time values; function names and interval syntax are dialect-specific.
CURRENT_DATE · CURRENT_TIMESTAMP · vendor date functionsOpen guide Query
SQL String functions
Transform or inspect strings; function names vary by dialect.
CONCAT(...) · SUBSTRING(...) · LENGTH(...)Open guide Query
SQL Aggregate functions
Summarize groups with COUNT, SUM, AVG, MIN and MAX.
COUNT(*) · SUM(expression) · AVG(expression) · MIN(...) · MAX(...) Open guide Schema
SQL Temporary tables
Create temporary data that is scoped to a session or transaction depending on the engine.
CREATE TEMPORARY TABLE name (...);Open guide Administration
SQL CREATE TRIGGER
Run database logic in response to table events; trigger syntax varies substantially.
CREATE TRIGGER trigger_name ... ON table_name ...Open guide Administration
SQL Stored procedures and functions
Define reusable database-side logic using vendor-specific procedural languages.
CREATE PROCEDURE / CREATE FUNCTION ...Open guide Administration
SQL EXPLAIN ANALYZE
Execute a query and report actual plan statistics on engines that support it.
EXPLAIN ANALYZE query;Open guide Administration
SQL Information schema and catalogs
Query metadata views to inspect tables, columns and constraints.
SELECT ... FROM information_schema.tables / columns;Open guide Transactions
SQL SET TRANSACTION
Configure isolation or read/write behaviour within supported transaction contexts.
SET TRANSACTION ISOLATION LEVEL ...;Open guide Transactions
SQL Locks and SELECT FOR UPDATE
Coordinate concurrent access using row or table locks; syntax and isolation differ.
SELECT ... FOR UPDATE; -- support and clauses varyOpen guide Query
SQL CASE expressions
Use conditional logic inside queries and data changes.
CASE WHEN condition THEN result ELSE fallback ENDOpen guide Query
SQL EXISTS / NOT EXISTS
Test whether a subquery returns at least one row.
WHERE EXISTS (SELECT 1 FROM ... WHERE correlated_condition)Open guide No matching entries. Try another search.