Underscore (‘ %’) WILDCARD with ESCAPE Clause In the above example, Oracle optimizer considers ‘_’ as a character, not as a WILDCARD because of the ESCAPE clause. SELECT Department FROM Dept_Category WHERE Department LIKE '%\_%' ESCAPE ‘\’ Underscore (‘ _’) WILDCARD with ESCAPE Clause ESCAPE clause has to be used along with ‘ \’. To fix this issue/drawback Oracle provides ESCAPE Clause.ĮSCAPE Clause: ESCAPE clause is used to find the exact match for ‘_’ & ‘%’ as a character.
In the above two examples, Oracle Optimizer considers _ & % as a WILDCARD, not a character.Why this issue occurred when we used correct syntax in the above two examples? The above SELECT statement returns all rows from the Dept_Category table but the expected result was the record(s) which consists only ‘%’ character because of the WILDCARD condition. SELECT deptno, dname, loc FROM Dept WHERE dname LIKE ‘%%%’ The above SELECT statement returns all rows from the Dept_Category table but the expected result was the record(s) which consists only ‘_’ character because of the WILDCARD condition. SELECT Department FROM Dept_Category WHERE Department LIKE '%_%' And returns the matching pattern as a result. So this statement having NOT keyword with WILCARD, which means it searches the entry in the Designation column which does not consist the second character ‘O’, but the first character can be anything.
SELECT Name, Designation, DOJ, Salary FROM Employee WHERE Designation NOT LIKE '_O%' Underscore ( ‘_’) WILDCARD with NOT keyword So this statement searches the entry in the Designation column which is having the second character ‘O’, but the first character can be anything. SELECT Name, Designation, DOJ, Salary FROM Employee WHERE Designation LIKE '_O%'Īs underscore (‘_’) WILDCARD represents any single character at the specified position. It means it selects the entries from Name column which consists of ‘E’ character at least once at any position and displays the records. In this example, % WILDCARD is being used twice after and before “E”. SELECT Name, Designation, DOJ, Salary FROM Employee WHERE Name LIKE '%E%' It means this SQL statement selects only those records which does not start with the supplied pattern ‘B’ with % WILCARD. In this output, two records are missing, WHY?īecause the above SELECT statement contains NOT keyword with WILDCARD and LIKE operator. SELECT Name, Designation, DOJ, Salary FROM Employee WHERE Name NOT LIKE 'B%' % represents any sequence of any number of characters including zero. The SQL statement fetched ‘CHANDAN’ details because in the Name column only CHANDAN starts with the “CH” character. It returns only those records which name begins with character pattern “CH” in the Name column and returns the matched record(s). In the above SELECT statement % WILDCARD with LIKE operator filter the record(s) based on the condition. SELECT Name, Designation, DOJ, Salary FROM Employee WHERE Name LIKE 'CH%'
For that, we will use the below sample table (Employee & Dept_category) with 14 & 8 records to understand the Oracle WILDCARDS behavior. In this section, we’ll see the implementation of Oracle WILDCARDS and its behavior. Implementations of WILDCARDS with Examples
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