如何爲Amazon Redshift數據庫編寫查詢，以使相關查詢的where子句具有兩個條件？

Question

示例 -

SELECT date, name, 
     (SELECT value 
     FROM this_table 
     WHERE col1= 'test1' and col2='test' 
     ) AS num_sloths_bought_before 
FROM source_table; 

當我執行在紅移查詢，我得到這個錯誤 -

[Amazon](500310) Invalid operation: This type of correlated subquery pattern is not supported yet; 

Answer 1

您通常可以使用連接重寫相關標量子查詢，對查詢它的左連接：

SELECT date, name, dt.value AS num_sloths_bought_before 
FROM source_table 
LEFT JOIN 
(SELECT val, 
     value 
    FROM this_table 
    WHERE col2='test' 
) this_table 
ON source_table.val= this_table.val;