How to Perform Partial String Matching in SQL Joins using LIKE?

Joining Tables with LIKE in SQL

When performing a join, you may encounter scenarios where the matching condition requires partial string matching using the LIKE operator. This involves matching a column in one table against a column in another table, where the corresponding values can have characters preceding or trailing them.

To address this, you can employ several approaches:

Using INSTR:

This method utilizes the INSTR function, which checks if a substring exists within a string.

<code class="sql">SELECT *
FROM TABLE a
JOIN TABLE b ON INSTR(b.column, a.column) > 0</code>

Using LIKE:

Alternatively, you can use the LIKE operator with wildcards % to match any number of characters.

<code class="sql">SELECT *
FROM TABLE a
JOIN TABLE b ON b.column LIKE '%'+ a.column +'%'</code>

Using LIKE with CONCAT:

Another technique involves concatenating the % wildcards with the column value using the CONCAT function.

<code class="sql">SELECT *
FROM TABLE a
JOIN TABLE b ON b.column LIKE CONCAT('%', a.column ,'%')</code>

Case Insensitive Matching:

In all cases, it's recommended to convert the column values to uppercase before comparison to ensure case-insensitive matching.

<code class="sql">SELECT *
FROM (SELECT UPPER(a.column) 'ua'
         FROM TABLE a) a
JOIN (SELECT UPPER(b.column) 'ub'
         FROM TABLE b) b ON INSTR(b.ub, a.ua) > 0</code>

The choice of method will depend on factors such as efficiency and database compatibility. Consult the EXPLAIN plan output to determine the optimal approach. Note that the JOIN syntax is equivalent to the equivalent WHERE clause.

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