Equals(=) vs. LIKE for date data type

Question

First, I'm aware that the equals (=) operator is a "comparison operator compares two values for equality."  In other words, in an SQL statement, it won't return true unless both sides of the equation are equal.  For example:
SELECT * FROM Store WHERE Quantity = 200;
The LIKE operator "implements a pattern match comparison" that attempts to match "a string value against a pattern string containing wild-card characters."  For example:
SELECT * FROM Employees WHERE Name LIKE 'Chris%';
Here,
I query about date type data on ORACLE database, I found the following, when I write select statment in this way:
SELECT ACCOUNT.ACCOUNT_ID, ACCOUNT.LAST_TRANSACTION_DATE FROM ACCOUNT WHERE ACCOUNT.LAST_TRANSACTION_DATE LIKE '30-JUL-07';
I get all rows I'm looking for. but when I use the sign equal = instead :
SELECT ACCOUNT.ACCOUNT_ID, ACCOUNT.LAST_TRANSACTION_DATE FROM ACCOUNT WHERE ACCOUNT.LAST_TRANSACTION_DATE = '30-JUL-07';
I get nothing even though nothing is different except the equal sign. Can I find any explanation for this please ?

Answer 1

You are relying on implicit datatype conversions between DATE and VARCHAR2.  This is not only bad practice but it's unreliable as it depends on NLS_DATE_FORMAT parameter settings.
My NLS_DATE_FORMAT parameter is different from yours, so if I do the same sort of test...
SQL> select * from emp;
     EMPNO ENAME      JOB              MGR HIREDATE                    SAL       COMM     DEPTNO
      7369 SMITH      CLERK           7902 17-DEC-1980 00:00:00        800                    20
      7499 ALLEN      SALESMAN        7698 20-FEB-1981 00:00:00       1600        300         30
      7521 WARD       SALESMAN        7698 22-FEB-1981 00:00:00       1250        500         30
      7566 JONES      MANAGER         7839 02-APR-1981 00:00:00       2975                    20
      7654 MARTIN     SALESMAN        7698 28-SEP-1981 00:00:00       1250       1400         30
      7698 BLAKE      MANAGER         7839 01-MAY-1981 00:00:00       2850                    30
      7782 CLARK      MANAGER         7839 09-JUN-1981 00:00:00       2450                    10
      7788 SCOTT      ANALYST         7566 19-APR-1987 00:00:00       3000                    20
      7839 KING       PRESIDENT            17-NOV-1981 00:00:00       5000                    10
      7844 TURNER     SALESMAN        7698 08-SEP-1981 00:00:00       1500          0         30
      7876 ADAMS      CLERK           7788 23-MAY-1987 00:00:00       1100                    20
      7900 JAMES      CLERK           7698 03-DEC-1981 00:00:00        950                    30
      7902 FORD       ANALYST         7566 03-DEC-1981 00:00:00       3000                    20
      7934 MILLER     CLERK           7782 23-JAN-1982 00:00:00       1300                    10
14 rows selected.
SQL> select * from emp where hiredate like '19-APR-87';
no rows selected
SQL> select * from emp where hiredate = '19-APR-87';
no rows selected
The LIKE operator is intended to be used for strings... DON'T attempt to use them on dates, and remember when you specify dates that you need to use TO_DATE (or the DATE internal format) to convert your string to DATE datatype
e.g.
SQL> select * from emp where hiredate = date '1987-04-19';
     EMPNO ENAME      JOB              MGR HIREDATE                    SAL       COMM     DEPTNO
      7788 SCOTT      ANALYST         7566 19-APR-1987 00:00:00       3000                    20