ORACLE SQL語句中的“SWITCH語句”函式DECODE
阿新 • • 發佈:2019-02-08
下面這個例子介紹ORACLE SQL Functions對DECODE函式的用法,引自官方文件
SELECT product_id,
DECODE (warehouse_id, 1, 'Southlake',
2, 'San Francisco',
3, 'New Jersey',
4, 'Seattle',
'Non domestic')
"Location of inventory" FROM inventories
WHERE product_id < 1775;
判斷每個滿足條件的記錄的warehouse_id,等於1,則返回'Southlake'...依次類推, 最後一個'Non domestic'是預設值。
功能跟跟SWITCH CASE很類似,但JAVA中的SWITCH條件是“Only int values or enum constants are permitted”所以JAVA中直接用字串是不可以作SWITCH條件的必須轉換為列舉型。
程式碼如下:
/**
* @author Milo
*
*/
public class SwitchTest {
public enum EnumType {YachunMiao, SanZhang}
/**
*
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
switch (EnumType.YachunMiao) {
case YachunMiao:
System.out.println("YachunMiao");
break;
case SanZhang:
System.out.println("SanZhang");
break;
default:
System.out.println("SiLi");
}
}
}
但ORACLE的DECODE函式可以直接用字串條件!
例如:
SELECT DECODE(SUBSTR('MIAOYACHUN',1, 4), 'MIAO', 'It is MIAO!','It is not MIAO!') FROM DUAL;
SELECT product_id,
DECODE (warehouse_id, 1, 'Southlake',
2, 'San Francisco',
3, 'New Jersey',
4, 'Seattle',
'Non domestic')
"Location of inventory" FROM inventories
WHERE product_id < 1775;
判斷每個滿足條件的記錄的warehouse_id,等於1,則返回'Southlake'...依次類推, 最後一個'Non domestic'是預設值。
功能跟跟SWITCH CASE很類似,但JAVA中的SWITCH條件是“Only int values or enum constants are permitted”所以JAVA中直接用字串是不可以作SWITCH條件的必須轉換為列舉型。
程式碼如下:
/**
* @author Milo
*
*/
public class SwitchTest {
public enum EnumType {YachunMiao, SanZhang}
/**
*
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
switch (EnumType.YachunMiao) {
case YachunMiao:
System.out.println("YachunMiao");
break;
case SanZhang:
System.out.println("SanZhang");
break;
default:
System.out.println("SiLi");
}
}
}
但ORACLE的DECODE函式可以直接用字串條件!
例如:
SELECT DECODE(SUBSTR('MIAOYACHUN',1, 4), 'MIAO', 'It is MIAO!','It is not MIAO!') FROM DUAL;