How to Construct Query-Derived Column Names Dynamically in MySQL?

Creating Query-Derived Column Names with MySQL concat()

In MySQL, it may be desirable to construct column names dynamically by concatenating strings with the results of another query. This approach can provide flexibility and customization when generating database objects. However, directly concatenating column names within a query may not produce the intended result.

Consider the following example:

<code class="sql">SELECT CONCAT('column', mytable.mycolumn) FROM table ...</code>

This query attempts to concatenate the string 'column' with the column 'mycolumn' from the 'table' table. However, it may not provide the expected output due to limitations in MySQL's handling of dynamic column names.

To overcome this issue, server-side prepared statements can be utilized to dynamically construct and execute SQL statements from strings. Here is an example that demonstrates how to create query-derived column names using prepared statements:

<code class="sql">set @query := (
  select concat(
    "select",
      group_concat(concat("\n  1 as ", column_name) separator ','),
    "\nfrom dual")
  from information_schema.columns
  where table_name = 'columns')
;
prepare s1 from @query
;
execute s1
;</code>

In this example:

• The variable '@query' is assigned a dynamic SQL query that constructs a 'SELECT' statement with column names generated from the 'column_name' column of the 'INFORMATION_SCHEMA.COLUMNS' table.
• The prepared statement 's1' is created from the '@query' variable.
• The 'EXECUTE s1' statement executes the prepared statement, creating and executing the dynamic SQL query.

This approach allows for the creation of query-derived column names on the fly, providing flexibility and customization in database operations.

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