Question

大家好我在从表中选择一些数据然后根据表1中的字段值将表连接到另一个表时遇到一个简单的问题

就像我有 table1 ， table2 和表3 。我想

<g:form controller="animais"> <g:hiddenField name="rootNode" value="${rootNode}"/> <g:hiddenField name="finalAnswer" value="${finalAnswer}"/> <h3>${curQuestion} </h3> <g:if test="${finished}"> <g:actionSubmit class="btn btn-primary" action="backToStart" value="Voltar" /> </g:if> <g:if test="${!finished}"> <g:if test="${!showDivTip}"> <g:textField name="finalAnswer" value="${finalAnswer}"/> <g:actionSubmit class="btn btn-primary" action="submitFinalAnswer" value="OK" /> </g:if> <g:if test="${showDivTip}"> <g:textField name="tipToFinalAnswer" value="${tipText}"/> <g:actionSubmit class="btn btn-primary" action="submitTipForAnswer" value="Finalizar" /> </g:if> </g:if> </g:form>。

我现在可以这样做，但我不是那么可以用它来帮助我解决问题..

Answer 1

我认为可以使用UNION调用来实现：

SELECT t2.f1, t2.f2, t2.f3
FROM table2 t2
INNER JOIN table1 t1
    ON t1.f1 = t2.f1
WHERE t2.f3 = 1

UNION ALL

SELECT t3.f1, t3.f2, t3.f3
FROM table3 t3
INNER JOIN table1 t1
    ON t1.f1 = t3.f1

Answer 2

试试这个：

SELECT t1.field1 AS t1field1, 
       t1.field2 AS t1field2, 
       CASE WHEN t1.field3 = 1 THEN t2.field1 ELSE t3.field1 END AS t2t3field1, 
       CASE WHEN t1.field3 = 1 THEN t2.field2 ELSE t3.field2 END AS t2t3field2, 
       CASE WHEN t1.field3 = 1 THEN t2.field3 ELSE t3.field3 END AS t2t3field3
FROM table1 t1 
LEFT JOIN table2 t2 ON t1.field1 = t2.field1
LEFT JOIN table3 t3 ON t1.field1 = t3.field1;

在mysqli中用于选择和加入的案例用法

2 个答案: