T-SQL添加行以零如果數據不存在

Question

我知道這個問題已經回答了幾次，但我仍然有麻煩添加一個額外的行，而數據不存在，直到它。

DECLARE @Test TABLE 

(
ID NVARCHAR(10) 
,Number INT 

) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',2) 
INSERT INTO @Test VALUES ('QD65',2) 
INSERT INTO @Test VALUES ('QD65',3) 
INSERT INTO @Test VALUES ('QD65',3) 
INSERT INTO @Test VALUES ('HT76',7) 
INSERT INTO @Test VALUES ('HT76',1) 
INSERT INTO @Test VALUES ('HT76',5) 

SELECT CASE WHEN ID = 'TG32' THEN 'Hats' 
      WHEN ID = 'QD65' THEN 'Coats' 
      WHEN ID = 'HT76' THEN 'Shoes' 
      WHEN ID = 'WR52' THEN 'Shirts' END 
      , Number 


FROM @Test 

我想在這說襯衫0的結果得到一個額外的行，而沒有用於ID WR52沒有數據，直到有？

Answer 1

試試這個

DECLARE @Test TABLE 
(
ID NVARCHAR(10) 
,Number INT 

) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',2) 
INSERT INTO @Test VALUES ('QD65',2) 
INSERT INTO @Test VALUES ('QD65',3) 
INSERT INTO @Test VALUES ('QD65',3) 
INSERT INTO @Test VALUES ('HT76',7) 
INSERT INTO @Test VALUES ('HT76',1) 
INSERT INTO @Test VALUES ('HT76',5) 

-- 
SELECT CASE WHEN ID = 'TG32' THEN 'Hats' 
      WHEN ID = 'QD65' THEN 'Coats' 
      WHEN ID = 'HT76' THEN 'Shoes' 
      WHEN ID = 'WR52' THEN 'Shirts' END 
      , Number 
FROM @Test 

UNION ALL 

SELECT 'Shirts', 0 
WHERE 
    NOT EXISTS 
    (
     SELECT TOP 1 1 FROM @Test 
     WHERE 
      ID = 'WR52' 
    ) 

UNION ALL 

SELECT 'Hats', 0 
WHERE 
    NOT EXISTS 
    (
     SELECT TOP 1 1 FROM @Test 
     WHERE 
      ID = 'TG32' 
    ) 


UNION ALL 

SELECT 'Coats', 0 
WHERE 
    NOT EXISTS 
    (
     SELECT TOP 1 1 FROM @Test 
     WHERE 
      ID = 'QD65' 
    ) 

UNION ALL 

SELECT 'Shoes', 0 
WHERE 
    NOT EXISTS 
    (
     SELECT TOP 1 1 FROM @Test 
     WHERE 
      ID = 'HT76' 
    ) 

Answer 2

你可以聲明第二個表並使用左連接，以確保您的類別總是出現。

DECLARE @Test TABLE (ID NVARCHAR(10),Number INT) 

INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',6) 
INSERT INTO @Test VALUES ('TG32',2) 
INSERT INTO @Test VALUES ('QD65',2) 
INSERT INTO @Test VALUES ('QD65',3) 
INSERT INTO @Test VALUES ('QD65',3) 
INSERT INTO @Test VALUES ('HT76',7) 
INSERT INTO @Test VALUES ('HT76',1) 
INSERT INTO @Test VALUES ('HT76',5) 

DECLARE @Categories TABLE (ID NVARCHAR(10), Item NVARCHAR(10)) 
INSERT INTO @Categories (ID, Item) VALUES 
    ('TG32', 'Hats'), 
    ('QD65', 'Coats'), 
    ('HT76', 'Shoes'), 
    ('WR52', 'Shirts') 

SELECT C.Item, ISNULL(S.Number, 0) AS 'Number' 
FROM @Categories C 
LEFT JOIN @Test S ON C.ID = S.ID 

這種方式，你只需要在一個地方添加一個新的類別，而不必手動列出類別沒有任何項目。

此外，你也許希望得到每個項目的總數。你能做到這一點，像這樣：

SELECT C.Item, SUM(ISNULL(S.Number, 0)) AS 'Number' 
FROM @Categories C 
LEFT JOIN @Test S ON C.ID = S.ID 
GROUP BY C.Item 

Answer 3

SELECT 
    CASE 
    WHEN ID = 'TG32' THEN 'Hats' 
    WHEN ID = 'QD65' THEN 'Coats' 
    WHEN ID = 'HT76' THEN 'Shoes' 
    WHEN ID = 'WR52' THEN 'Shirts' 
    END AS 'Item', 
    Number 
FROM @Test 
UNION ALL 
SELECT 
    'Shirts', 
    0 

Answer 4

這看起來像你應該使用一個單獨的查找表Id值映射到Item值的情況。

-- Sample data. 
declare @Test as Table (Id NVarChar(10), Number Int); 
insert into @Test (Id, Number) values 
    ('TG32',6), ('TG32',6), ('TG32',6), ('TG32',2), ('QD65',2), 
    ('QD65',3), ('QD65',3), ('HT76',7), ('HT76',1), ('HT76',5); 
select * from @Test; 

-- Using a CTE with a lookup table. 
with ProductLookup as (
    select ProductCode, Item 
    from (values ('TG32', 'Hats'), ('QD65', 'Coats'), ('HT76', 'Shoes'), ('WR2', 'Shirts')) as 
     Alpha(ProductCode, Item)) 
    select PL1.Item, T.Number 
    from @Test as T inner join 
     ProductLookup as PL1 on PL1.ProductCode = T.Id 
    union all 
    select Item, 0 
    from ProductLookup as PL2 
    where not exists (select 42 from @Test where Id = PL2.ProductCode); 

注意，該解決方案將產生一個「零」行了任何缺少的產品類型：同樣的結果可以使用公用表表達式（CTE）來創建一個查找表用非常短的壽命可以了，不只是襯衫。

假設：您正在使用SQL Server 2005或更高版本。使用適當的軟件（MySQL，Oracle，DB2，...）和版本（例如， sql-server-2014。