Oracle Decode函数

   

      DECODE函数相当于一条件语句(IF).它将输入数值与函数中的参数列表相比较，根据输入值返回一个对应值。有兴趣的可以看看下面的例子。

 

 

Note: Decode and Case are very similar in their appearance but can produce very different results.

Demo Tables & Data

Airplanes Table

Locations Table

All other tables

DECODE (overload 1)

standard.decode(expr NUMBER, pat NUMBER, res NUMBER) RETURN NUMBER;

DECODE (overload 2)

standard.decode(
expr NUMBER,
pat  NUMBER,
res  VARCHAR2 CHARACTER SET ANY_CS)
return VARCHAR2 CHARACTER SET res%CHARSET;

DECODE (overload 3)

standard.decode(expr NUMBER, pat NUMBER, res DATE) RETURN DATE;

DECODE (overload 4)

standard.decode(
expr VARCHAR2 CHARACTER SET ANY_CS,
pat  VARCHAR2 CHARACTER SET expr%CHARSET,
res  NUMBER)
RETURN NUMBER;

DECODE (overload 5)

standard.decode(
expr VARCHAR2 CHARACTER SET ANY_CS,
pat  VARCHAR2 CHARACTER SET expr%CHARSET,
res  VARCHAR2 CHARACTER SET ANY_CS)
RETURN VARCHAR2 CHARACTER SET res%CHARSET;

DECODE (overload 6)

standard.decode(
expr VARCHAR2 CHARACTER SET ANY_CS,
pat  VARCHAR2 CHARACTER SET expr%CHARSET,
res  DATE)
RETURN DATE;

DECODE (overload 7)

standard.decode(expr DATE, pat DATE, res NUMBER) RETURN NUMBER;

DECODE (overload 8)

standard.decode(
expr DATE,
pat  DATE,
res  VARCHAR2 CHARACTER SET ANY_CS)
RETURN VARCHAR2 CHARACTER SET res%CHARSET;

DECODE (overload 9)

standard.decode( expr DATE, pat DATE, res DATE) RETURN DATE;

DECODE (overload 10)

standard.decode(expr OBJECT, pat  OBJECT, res OBJECT) RETURN OBJECT;

DECODE (overload 11)

standard.decode(expr UNDEFINED, pat UNDEFINED, res UNDEFINED)
RETURN UNDEFINED;

Simple DECODE

SELECT DECODE (value, , )
FROM dual;

SELECT program_id, 
  DECODE(customer_id, 'AAL', 'American Airlines') AIRLINE,
  delivered_date
FROM airplanes
WHERE ROWNUM < 11;

More Complex DECODE

SELECT DECODE (value,<if this value>,<return this value>,
                     < if this value>,<return this value>,
                      ....)
FROM dual;

SELECT program_id,
       DECODE(customer_id,
              'AAL', 'American Airlines',
              'ILC', 'Intl. Leasing Corp.',
              'NWO', 'Northwest Orient',
              'SAL', 'Southwest Airlines',
              'SWA', 'Sweptwing Airlines',
              'USAF', 'U.S. Air Force') AIRLINE,
       delivered_date
FROM airplanes
WHERE ROWNUM < 11;

DECODE with DEFAULT

SELECT DECODE (value,,,
                     ,,
                     ....
                     )
FROM dual;

SELECT program_id,
       DECODE(customer_id,
             'AAL', 'American Airlines',
             'ILC', 'Intl. Leasing Corp.',
             'NWO', 'Northwest Orient',
             'SAL', 'Southwest Airlines',
             'SWA', 'Sweptwing Airlines',
             'USAF', 'United States Air Force',
             'Not Known') AIRLINE,
       delivered_date
FROM airplanes
WHERE ROWNUM < 11;

Note: The following crosstabulation is the standard for 10g or earlier. In 11g use the PIVOT and UNPIVOT operators

Simple DECODE Crosstab

Note how each decode only looks at a single possible value and turns it into a new column

SELECT program_id,
       DECODE(customer_id, 'AAL', 'AAL') AMERICAN,
       DECODE(customer_id, 'DAL', 'DAL') DELTA,
       DECODE(customer_id, 'NWO', 'NWO') NORTHWEST,
       DECODE(customer_id, 'ILC', 'ILC') INTL_LEASING
FROM airplanes
WHERE rownum < 20;

DECODE as an in-line view with crosstab summation

The above DECODE, in blue, used as an in-line view

SELECT program_id,
       COUNT (AMERICAN) AAL,
       COUNT (DELTA) DAL,
       COUNT (NORTHWEST) NWO,
       COUNT(INTL_LEASING) ILC
FROM (
   SELECT program_id,
          DECODE(customer_id, 'AAL', 'AAL') AMERICAN,
          DECODE(customer_id, 'DAL', 'DAL') DELTA,
          DECODE(customer_id, 'NWO', 'NWO') NORTHWEST,
          DECODE(customer_id, 'ILC', 'ILC') INTL_LEASING
   FROM airplanes)
GROUP BY program_id;

Query for DECODE demo

CREATE TABLE stores (
store_name      VARCHAR2(20),
region_dir      NUMBER(5),
region_mgr      NUMBER(5),
store_mgr1      NUMBER(5),
store_mgr2      NUMBER(5),
asst_storemgr1  NUMBER(5),
asst_storemgr2  NUMBER(5),
asst_storemgr3  NUMBER(5));

INSERT INTO stores 
VALUES ('San Francisco',100,200,301,302,401,0,403);

INSERT INTO stores
VALUES ('Oakland',100,200,301,0,404,0,0);

INSERT INTO stores
VALUES ('Palo Alto',100,200,0,305,0,405,406);

INSERT INTO stores
VALUES ('Santa Clara',100,250,0,306,0,0,407);
COMMIT;

SELECT DECODE(asst_storemgr1, 0,
       DECODE(asst_storemgr2, 0,
       DECODE(asst_storemgr3, 0, 0, asst_storemgr3),
       asst_storemgr2), asst_storemgr1) ASST_MANAGER,
       DECODE(store_mgr1,0, DECODE(store_mgr2,0, 0, store_mgr2),
       store_mgr1) STORE_MANAGER,
       REGION_MGR,
       REGION_DIR
FROM stores;

DECODE with Summary Function

SELECT SUM(CA_COUNT) CA, SUM(TX_COUNT) TX
FROM (
   SELECT state,
   DECODE(state, 'CA', COUNT(*), 0) CA_COUNT,
   DECODE(state, 'TX', COUNT(*), 0) TX_COUNT
   FROM locations
   GROUP BY state);

DECODE in the WHERE clause

set serveroutput on

DECLARE
 posn  PLS_INTEGER := 0;
 empid PLS_INTEGER := 178;
 x     NUMBER;
BEGIN
  SELECT NVL(SUM(ah.quantity * ah.saleprice * ap.payoutpct), 0)
  INTO x
  FROM accessoryhistory ah, payoutpercentage ap, 
  sku s, store st
  WHERE empid = DECODE(posn, 
                          0, st.areadir,
                          1, st.areamgr,
                          2, NVL(st.storemgr1, st.storemgr2),
                          3, NVL(st.asstmgr1, NVL(st.asstmgr2,
                       st.asstmgr3)))
  AND ah.statustype IN ('ACT', 'DEA')
  AND ah.store = st.store
  AND s.dbid = ah.dbid
  AND s.sku = ah.sku
  AND ap.productgroup = s.productgroup
  AND ap.position = posn;

  dbms_output.put_line(x);
END;
/

DECODE Altered WHERE Clause

CREATE TABLE test (
pubdate  DATE,
compdate DATE,
valuecol NUMBER(5));

INSERT INTO test VALUES (TRUNC(SYSDATE), TRUNC(SYSDATE+300), 1);
INSERT INTO test VALUES (TRUNC(SYSDATE-300), TRUNC(SYSDATE), 9);
COMMIT;

SELECT * FROM test;

CREATE OR REPLACE PROCEDURE testproc (
StartDate DATE, EndDate DATE, DateType IN VARCHAR2) IS

 i PLS_INTEGER;
BEGIN
  SELECT valuecol
  INTO i
  FROM test
  WHERE DECODE(DateType, 'AA',compdate, 'BB', pubdate, compdate) <= EndDate
  AND DECODE(DateType, 'AA', compdate, 'BB', pubdate, compdate) >= StartDate;

  dbms_output.put_line(TO_CHAR(i));
END testproc;
/

set serveroutput on

exec testproc(TRUNC(SYSDATE), TRUNC(SYSDATE), 'BB');