Final answer:
The error ORA-01007 occurs when there is an attempt to fetch data into a variable that is not included in the SELECT statement of a SQL query within Oracle databases. This mismatch between expected results and the program's host variables is usually resolved by aligning the SELECT statement with all intended host variables.
Step-by-step explanation:
The error ORA-01007: variable not in select list occurs in Oracle database operations when a program attempts to fetch a column into a host variable, but the column is not part of the SELECT statement in the SQL query. This happens typically in PL/SQL programs or applications that use Oracle Call Interface (OCI) or Pro*C/C++ precompiler.
For example, if a PL/SQL block declares a host variable to hold a column value but the SELECT query does not include that column, then upon fetching the results, this error will be triggered. The resolution involves ensuring that all variables used in the program for storing result set values are matched with the corresponding columns in the SELECT statement.