MySQL CASE 和 RPAD 问题

Question

我在下面有这个查询，它运行良好。我只是不知道如何在 val_4 上使用 RPAD 函数。我尝试在 CASE 中使用 RPAD，但失败了。

SELECT RPAD(val_1,1,' '), RPAD(val_2,9,' '), RPAD(val_3,6,' '),
    (CASE val_4
        WHEN 'abc' THEN 'USEABLE'
        WHEN 'abcd' THEN 'USEABLE'
        WHEN 'abcde' THEN 'USEABLE'
        ELSE 'UNUSABLE'
    END)
FROM lists
INTO OUTFILE '/path/to/file'
FIELDS TERMINATED BY ''
LINES TERMINATED BY '\n';

Answer 1

包装整个案例:

SELECT RPAD(val_1,1,' '), RPAD(val_2,9,' '), RPAD(val_3,6,' '),
    RPAD(CASE val_4
        WHEN 'abc' THEN 'USEABLE'
        WHEN 'abcd' THEN 'USEABLE'
        WHEN 'abcde' THEN 'USABLE'
        ELSE 'abcdef'
    END, 6, ' ')
FROM lists
INTO OUTFILE '/path/to/file'
FIELDS TERMINATED BY ''
LINES TERMINATED BY '\n';

SQL Fiddle example

---

或者，只包装 val_4 的值:

SELECT RPAD(val_1,1,' '), RPAD(val_2,9,' '), RPAD(val_3,6,' '),
    CASE RPAD(val_4,4,' ')
        WHEN 'abc' THEN 'USEABLE'
        WHEN 'abcd' THEN 'USEABLE'
        WHEN 'abcde' THEN 'USABLE'
        ELSE 'abcdef'
    END
FROM lists
INTO OUTFILE '/path/to/file'
FIELDS TERMINATED BY ''
LINES TERMINATED BY '\n';

SQL Fiddle example