How to execute second query when first query has no results

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How to execute second query when first query has no results - MYSQL

P粉998100648 2023-09-16 16:12:30

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How to get results in MYSQL:

If the first selection has more than 0 rows, return the result, otherwise return the result of the second selection ( is not the same table , there is only one column in the two selections).

Something similar SELECT IF ((EXISTS(SELECT COLUMN 1 FROM TABLE 1)),(SELECT COLUMN 1 FROM TABLE 1),(SELECT COLUMN 1 FROM TABLE 2);

P粉998100648

reply all(1)

P粉3421016522023-09-17 12:14:43 1 floor

You can use the joint trick here:

WITH cte AS (
    SELECT Column1, 1 AS pos FROM Table1
    UNION ALL
    SELECT Column1, 2 FROM Table2
)

SELECT Column1
FROM cte
WHERE
    pos = 1 OR
    NOT EXISTS (SELECT 1 FROM cte WHERE pos = 1);