如何使用是/否缩写检索多个表的数据

Question

我有5张桌子

Village

 T1_Master (Village_ID is a foreign key)

T2_Master (Village_ID is a foreign key)

T1_Details (t1_id is a foreign key) & (month,year,t1_id are combination of primary key（复合密钥））

T2_Details (t2_id is a foreign key) & (month,year,t2_id are combination of primary key（复合键））

现在，如果我想要检索village_ID = 01, month=03 and year=2013

的记录

然后输出应该如下

here t1_1(No) = t1_1 has no record for month=03 and year=2013

Like wise t2_1(Yes) = t2_1 has record for month=03 and year=2013等等......

Plz帮助我.... plz

Answer 1

我认为你想要一个或多个LEFT或RIGHT JOIN：

 SELECT
    V.Village_ID    
    , Dates.[MONTH]
    , Dates.[YEAR]
    , CASE WHEN colValue IS NULL THEN 'no'
         ELSE 'yes'
         END [Yes or No]
FROM
    (
    SELECT
       Village_ID
    FROM 
        Villages
    WHERE
        Village_ID = @ParamVilageID
    ) V
    LEFT JOIN
    (
    SELECT
        Viilage_ID
        , [MONTH]
        , [YEAR]
    FROM
        T1_Details
    WHERE
        [MONTH] = @ParamMonth
        AND
        [YEAR] = @ParamYear
    ) Dates
    ON V.Village_ID = Dates.Village_ID

您需要决定将哪个列引用为colValue，但所有SQL元素都在那里。 SQL将根据案例陈述推断数据类型（字符串），但您也可以返回一个直布尔值0或1

顺便说一句，拥有一个smallDate列会好得多，因为SQL有DatePart和DateName函数

Answer 2

您需要使用外连接来获取空值（您可能需要考虑在左连接上找到一些可用的教程 - 很多都在谷歌上）。关键是当详细信息行不可用时使用主表来显示id。

SELECT  v.Village_id, 
        CASE WHEN t1d.t1_id IS NULL THEN CAST(t1m.t1_id AS VARCHAR(50)) + ' (No)'
                ELSE CAST(t1m.t1_id AS VARCHAR(50)) + ' (Yes)'
        END T1,
        CASE WHEN t2d.t2_id IS NULL THEN CAST(t2m.t2_id AS VARCHAR(50)) + ' (No)'
                ELSE CAST(t2m.t2_id AS VARCHAR(50)) + ' (Yes)'
        END T2
FROM Village v 
        LEFT OUTER JOIN T1_Master t1m
        ON t1m.Village_ID = v.Village_ID
        LEFT OUTER JOIN T1_Details t1d
        ON t1d.t1_id = t1m.t1_id
            AND t1d.[month] = 03
            AND t1d.[year] = 2013
        LEFT OUTER JOIN T2_Master t2m
        ON t2m.Village_ID = v.Village_ID
        LEFT OUTER JOIN T2_Details t2d
        ON t2d.t2_id = t2m.t2_id
            AND t2d.[month] = 03
            AND t2d.[year] = 2013
WHERE v.Village_ID = 01

根据数据库中的空值设置，CAST(t2m.t2_id AS VARCHAR(50)) + ' (No)'语句可能需要检查t2m记录是否为空以使其显示为空而不是仅显示“（否）”