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mysql 中的分支函数, 用来获得指定值
格式是
case kx when k1 then v1 when k2 then v2 else vn end;
其中, selse 是可选的部分, when .. then .. 至少要有一个
mysql> select case 2 when 1 then 1 when 2 then 2 end; +----------------------------------------+ | case 2 when 1 then 1 when 2 then 2 end | +----------------------------------------+ | 2 | +----------------------------------------+ 1 row in set (0.00 sec) mysql> select case 'b' when 1 then 1 when 'b' then 'b' else 'c' end; +--------------------------------------------------------+ | case 'b' when 1 then 1 when 'b' then 'b' else 'c' end | +--------------------------------------------------------+ | b | +--------------------------------------------------------+ 1 row in set, 1 warning (0.03 sec) mysql> select case 'z' when 1 then 1 when 'b' then 'b' else 'c' end; +--------------------------------------------------------+ | case 'z' when 1 then 1 when 'b' then 'b' else 'c' end | +--------------------------------------------------------+ | c | +--------------------------------------------------------+ 1 row in set, 1 warning (0.00 sec)
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