#解释一下这个sql
SELECT @xi:=@xi+1 as xc from
(SELECT 1 UNION SELECT 2 UNION SELECT 3 ) xc1,
(SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) xc2,
(SELECT @xi:=0) xc0;
#解释一下这个sql
SELECT @xi:=@xi+1 as xc from
(SELECT 1 UNION SELECT 2 UNION SELECT 3 ) xc1,
(SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) xc2,
(SELECT @xi:=0) xc0;