Question

它可能类似于之前的问题，但它略有不同（它现在有字段id变量）

我有以下表格。

表1

 ID1   YEAR1        
 1      1980  
 2      1964 
 3      1910

和表2

 ID2  YEAR2   VALUE FIELD ID
 1     2000     A     324
 1     1900     B     345
 2     1950     C     123
 2     1900     B     324
 3     2000     C     123
 3     1970     B     444
 4     1900     D     324
 4     1800     E     123

我想加入/查询这些表格：

对于表1中的每个ID1匹配，添加一个名为VALUE的列 - 因此列名称将为A，B，...等等，该列将为TRUE（T）或FALSE（F）。

如果ID1与表2中的ID2匹配，则列A ...将为TRUE，表2中与ID2匹配的给定行的YEAR2小于表1给出id1和VALUE的YEAR1从表2中具有ID2的行得到A并且FIELD ID是324或123

所以结果表如下：

ID1   YEAR1     A   B   C   D   E         

 1      1980    F   F   F   F   F 
 2      1964    F   T   T   F   F 
 3      1910    F   F   F   F   F

...

谢谢：）

Answer 1

SELECT DISTINCT t1.id1,
       t1.year1,
       CASE WHEN t1.id1 = t2.id2 AND t2.value = 'A' AND t2.year2 <= t1.year1 THEN 'T' ELSE 'F' END AS A,
       CASE WHEN t1.id1 = t2.id2 AND t2.value = 'B' AND t2.year2 <= t1.year1 THEN 'T' ELSE 'F' END AS B,
       CASE WHEN t1.id1 = t2.id2 AND t2.value = 'C' AND t2.year2 <= t1.year1 THEN 'T' ELSE 'F' END AS C,
       CASE WHEN t1.id1 = t2.id2 AND t2.value = 'D' AND t2.year2 <= t1.year1 THEN 'T' ELSE 'F' END AS D,
       CASE WHEN t1.id1 = t2.id2 AND t2.value = 'E' AND t2.year2 <= t1.year1 THEN 'T' ELSE 'F' END AS E
  FROM table1 t1
INNER JOIN
       table2 t2
    ON t1.id1 = t2.id2;

有效地进行SQL查询或加入POSTGRES的方法？

1 个答案: