我正在查看一些舊的 PL/SQL 代碼，我有十幾個這樣撰寫的 DECODE 函式：
DECODE(value_1, value_2, 1, 0) = 0
現在，我知道這些解碼器在value_1和value_2之間進行比較，它們根據比較的結果回傳 true 或 false。但是，對于編碼的熱愛，有人可以告訴我= 0部分背后的邏輯是什么嗎？為什么需要檢查回傳值是否為 0？
uj5u.com熱心網友回復：
- 如果
value_1 = value_2，則解碼回傳1 - 否則，它回傳
0
因此，整個運算式檢查是否value_1不同于value_2然后 - 我推測 -做某事。
如果它是 PL/SQL 的一部分，您可以將其重寫為
if value_1 <> value_2 then...
一些例子：
SQL> declare
2 value_1 number := 5;
3 value_2 number := 1;
4 begin
5 decode(value_1, value_2, 1, 0) = 0
6 end;
7 /
decode(value_1, value_2, 1, 0) = 0
*
ERROR at line 5:
ORA-06550: line 5, column 34:
PLS-00103: Encountered the symbol "=" when expecting one of the following:
:= . ( % ;
SQL> declare
2 value_1 number := 5;
3 value_2 number := 1;
4 begin
5 decode(value_1, value_2, 1, 0) = 0;
6 end;
7 /
decode(value_1, value_2, 1, 0) = 0;
*
ERROR at line 5:
ORA-06550: line 5, column 34:
PLS-00103: Encountered the symbol "=" when expecting one of the following:
:= . ( % ;
The symbol ":= was inserted before "=" to continue.
SQL> declare
2 value_1 number := 5;
3 value_2 number := 1;
4 begin
5 if decode(value_1, value_2, 1, 0) = 0 then
6 null;
7 end if;
8 end;
9 /
if decode(value_1, value_2, 1, 0) = 0 then
*
ERROR at line 5:
ORA-06550: line 5, column 6:
PLS-00204: function or pseudo-column 'DECODE' may be used inside a SQL statement only
ORA-06550: line 5, column 3:
PL/SQL: Statement ignored
SQL> declare
2 value_1 number := 5;
3 value_2 number := 1;
4 begin
5 case when decode(value_1, value_2, 1, 0) = 0 then
6 null;
7 end case;
8 end;
9 /
case when decode(value_1, value_2, 1, 0) = 0 then
*
ERROR at line 5:
ORA-06550: line 5, column 13:
PLS-00204: function or pseudo-column 'DECODE' may be used inside a SQL statement only
ORA-06550: line 5, column 3:
PL/SQL: Statement ignored
SQL> declare
2 value_1 number := 5;
3 value_2 number := 1;
4 l_decode_result number;
5 begin
6 select decode(value_1, value_2, 1, 0)
7 into l_decode_result
8 from dual;
9 end;
10 /
PL/SQL procedure successfully completed.
SQL>
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