Αποτελέσματα Αναζήτησης
The UNION operator is a set operator that combines result sets of two or more SELECT statements into a single result set. The following illustrates the syntax of the UNION operator that combines the result sets of two queries: SELECT . column_list_1. FROM . T1. UNION SELECT . column_list_1. FROM . T2;
TABLE in Unions. Beginning with MySQL 8.0.19, you can also use a TABLE statement or VALUES statement in a UNION wherever you can employ the equivalent SELECT statement. Assume that tables t1 and t2 are created and populated as shown here:
UNION ALL Syntax. The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL: SELECT column_name (s) FROM table1. UNION ALL. SELECT column_name (s) FROM table2; Note: The column names in the result-set are usually equal to the column names in the first SELECT statement.
UNION combines the result from multiple SELECT statements into a single result set. Example: mysql> SELECT 1, 2; . +---+---+. | 1 | 2 |. +---+---+. | 1 | 2 |. +---+---+. mysql> SELECT 'a', 'b'; . +---+---+. | a | b |. +---+---+. | a | b |. +---+---+. mysql> SELECT 1, 2 UNION SELECT 'a', 'b'; . +---+---+. | 1 | 2 |. +---+---+. | 1 | 2 |.
25 Σεπ 2018 · The Union operator combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the Union. In simple terms, it combines the two or more row sets and keeps duplicates.
UNION combines the result from multiple query blocks into a single result set. This example uses SELECT statements: mysql> SELECT 1, 2; +---+---+ | 1 | 2 | +---+---+ | 1 | 2 | +---+---+ mysql> SELECT 'a', 'b'; +---+---+ | a | b | +---+---+ | a | b | +---+---+ mysql> SELECT 1, 2 UNION SELECT 'a', 'b'; +---+---+ | 1 | 2 | +---+---+ | 1 | 2 | | a ...
The following statement combines the results of two queries with the UNION operator, which eliminates duplicate selected rows. This statement shows that you must match data type (using the TO_CHAR function) when columns do not exist in one or the other table:
