ORACLE--SQL日常问题和技巧1（列变行、自定义查询结构、将字符串分割为多条记录）

  1.ORACLE列变行加合计：

查询结果为

SELECT
    nvl( F, '合计' ) F,
    sum( S1 ) S1,
    sum( S2 ) S2,
    sum( S3 ) S3
FROM
    (SELECT
    F,
    sum( decode( S, 'S1', N, NULL ) ) S1,
    　　 sum( decode( S, 'S2', N, NULL ) ) S2,
    　　 sum( decode( S, 'S3', N, NULL ) ) S3 　　 
FROM
    LQG_TEST 　　 
GROUP BY
    F)
GROUP BY
    rollup (
    F)

 2.自定义查询结构，场景如下：

查询语文，数学，英语，科学四门学科的分数，但是表里只有数学和英语。如图：

查询结果为：

看看SQL吧(nvl函数用于oracle)：

SELECT
    TMP1.COURSE AS COURSE,
    NVL ( TMP2.SCORE, 0 ) AS SCORE 
FROM
    (
    SELECT
        '语文' COURSE 
    FROM
    DUAL UNION ALL
    SELECT
        '数学' COURSE 
    FROM
    DUAL UNION ALL
    SELECT
        '英语' COURSE 
    FROM
    DUAL UNION ALL
    SELECT
        '科学' COURSE 
    FROM
    DUAL 
    ) TMP1
    LEFT JOIN (
    SELECT
    CASE
            
        WHEN
            COURSE = 'CHINESE' THEN
                '语文' 
                WHEN COURSE = 'MATH' THEN
                '数学' 
                WHEN COURSE = 'ENGLISH' THEN
                '英语' 
                WHEN COURSE = 'SCIENCE' THEN
                '科学' 
            END AS COURSE,
            SCORE 
        FROM
        LGQ_TEST 
    ) TMP2 ON TMP1.COURSE = TMP2.COURSE

 3.将字符串按某字符分割为多条记录

SELECT
    REGEXP_SUBSTR( '赵-钱-孙-李', '[^-]+', 1, ROWNUM ) 
FROM
    dual CONNECT BY ROWNUM <= LENGTH( '赵-钱-孙-李' ) - LENGTH(
    regexp_replace( '赵-钱-孙-李', '-', '' )) + 1