| Note: Decode and Case are very similar in their appearance but can produce very different results. |
| Demo Tables & Data |
|
| |
| Decode Built-in Function |
| Simple DECODE |
SELECT DECODE (value, <if this value>, <return this 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; |
| DEOCODE with DEFAULT |
SELECT DECODE (value,<if this value>,<return this value>,
<if this value>,<return this value>,
....
<otherwise 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', 'United States Airforce',
'Not Known') AIRLINE,
delivered_date
FROM airplanes
WHERE ROWNUM < 11; |
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))
TABLESPACE data_sml;
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;
/ |
| |
| Case Built-in Function |
| Simple CASE Demo |
SELECT CASE WHEN (<column_value> = <value>) THEN
WHEN (<column_value> = <value>) THEN
ELSE <value>
FROM <table_name>; |
SELECT line_number,
CASE WHEN (line_number = 1) THEN 'One'
WHEN (line_number = 2) THEN 'Two'
ELSE 'More Than Two'
END AS RESULTSET
FROM airplanes; |
| More Complex CASE Demo With Between |
SELECT CASE WHEN (<column_value> BETWEEN <value>
AND <value>) THEN
WHEN (<column_value>
BETWEEN <value> AND <value>) THEN
ELSE <value>
FROM <table_name>; |
SELECT line_number,
CASE WHEN (line_number BETWEEN 1 AND 10) THEN 'One'
WHEN (line_number BETWEEN 11 AND 100) THEN 'Big'
ELSE 'Bigger'
END
FROM airplanes; |
| More Complex CASE Demo With Booleans |
SELECT CASE WHEN (<column_value> <= <value>) THEN
WHEN (<column_value> <= <value>) THEN
ELSE <value>
FROM <table_name>; |
SELECT line_number,
CASE WHEN (line_number < 10) THEN 'Ones'
WHEN (line_number < 100) THEN 'Tens'
WHEN (line_number < 1000) THEN 'Hundreds'
ELSE 'Thousands'
END RESULT_SET
FROM airplanes; |
| The above demo turned into a view |
CREATE OR REPLACE VIEW line_number_view AS
SELECT line_number,
CASE WHEN (line_number < 10) THEN 'Ones'
WHEN (line_number < 100) THEN 'Tens'
WHEN (line_number < 1000) THEN 'Hundreds'
ELSE 'Thousands'
END RESULT_SET
FROM airplanes; |
| |
| CASE - DECODE Comparison |
| The same functionality written using both functions |
SELECT parameter, DECODE(SIGN(parameter-1000),-1,'C','P') AS BAND
FROM parameter_table;
SELECT parameter,
CASE WHEN parameter < 1000 THEN 'C' ELSE 'P' END AS BAND
FROM parameter_table; |