mysql - MySQL 选择表是否存在

Question

我需要对表运行计数查询，但前提是该表存在，

SELECT 
CASE WHEN (SELECT COUNT(*) FROM information_schema.TABLES WHERE TABLE_SCHEMA = 'DATABASENAME' AND TABLE_NAME = 'testtable') < 1 THEN '0' 
ELSE (SELECT COUNT(*) FROM testtable) END;

如果表不存在，上述查询应返回 0，但如果存在，则应获取计数。

这会返回一个错误，说“testtable”不存在，我们知道它不存在，因为 information_schema 计数返回 0。

这在 MySQL 中可能吗？

Answer 1

You can try this :

       SET @val := CASE (SELECT COUNT(*) FROM information_schema.TABLES WHERE TABLE_SCHEMA = 'DATABASENAME' AND TABLE_NAME = 'testtable')
           WHEN 0 THEN 0
           ELSE (SELECT COUNT(*) FROM information_schema.TABLES WHERE TABLE_SCHEMA = 'DATABASENAME' AND TABLE_NAME = 'testtable')

END;
        SELECT @val;

It will return 0, if there is no such table and if such table exists , it will return the count, it may be better if you take it into function.