Query

SQL UNION / UNION ALL

Combine compatible result sets; UNION removes duplicates while UNION ALL keeps them.

Availability: Common SQL with references for SQL standard, MySQL/MariaDB, PostgreSQL, SQL Server, SQLite and Oracle Database; syntax and feature support vary by engine and version.中文

Syntax

query_1 UNION [ALL] query_2;

Examples

Example (standard-style syntax). Verify supported keywords in your database.

SELECT email FROM customers UNION SELECT email FROM suppliers;

SQLite-oriented variant; dialect behaviour may differ.

SELECT email FROM customers UNION ALL SELECT email FROM suppliers;

Parameters, options and clauses

Option / clause	Description
`SELECT / expression`	Choose output columns, expressions, aliases or functions.
`FROM / JOIN`	Choose source tables and combine related rows.
`WHERE`	Filter rows before grouping; use IS NULL for null checks.
`GROUP BY / HAVING`	Group rows and filter aggregate groups.
`ORDER BY`	Sort the result; ASC is commonly the default and DESC reverses it.
`LIMIT / OFFSET / FETCH`	Limit or skip rows; syntax differs by database dialect.

Dialect references

Safety note

Review a command and its target before running it. Commands that alter files, services, accounts, disks, permissions or databases may be difficult to reverse. Test in a safe environment and keep backups.

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