MySQL將兩個表合並為一個

Question

我有兩個假想表：

1.人

id, age
1, 25

2.名稱

id, people_id, type, value
1, 1, 'first', 'John'
2, 1, 'last', 'Doe'

我如何才能將兩個表連接起來，以便得到以下結果：

id, age, first, last
1, 25, 'John', 'Doe'

Answer 1

SELECT  a.ID,
        a.Age,
        MAX(CASE WHEN b.type = 'first' THEN b.Value END) `First`,
        MAX(CASE WHEN b.type = 'last' THEN b.Value END) `Last`
FROM    People a
        LEFT JOIN Names b
            ON a.ID = b.people_id
GROUP   BY a.ID, a.Age

• SQLFiddle演示

否則，如果列type值未知，則動態語句更可取。

SET @sql = NULL;

SELECT  GROUP_CONCAT(DISTINCT
        CONCAT('MAX(CASE WHEN b.type = ''',
               type,
               ''' THEN value ELSE NULL END) AS ',
               CONCAT('`', type, '`')
               )) INTO @sql
FROM Names;

SET @sql = CONCAT('SELECT  a.ID,
                            a.Age, ', @sql , '
                    FROM    People a
                            LEFT JOIN Names b
                                ON a.ID = b.people_id
                    GROUP   BY a.ID, a.Age');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

• SQLFiddle演示

Answer 2

您正在尋找有關如何聯接來自不同表的數據的常規信息。 這稱為內部聯接。 參考可以在這里找到。

Answer 3

希望對您有幫助，

方法：1

 select p.id, p.age, n.type as first, n.value as last from People as p, Names as n where p.id = n.people_id

方法：2

 select p.id, p.age, n.type as first, n.value as last from People as p LEFT JOIN Names as n ON p.id = n.people_id 

Answer 4

SELECT p.id, p.age, n.first, n.last
FROM People p
JOIN Names n 
ON p.id = n.people_id;