You can include the following control logic in the SQL queries
WHILE loops
If.. elseif.. else... endif blocks
The syntax of while loops is as follows
WHILE expression;
<statements>
WEND
The syntax of IF statements is as follows
IF expression
<statements>
optionally one or more blocks
ELSEIF expression
<statements>
optionally
ELSE
<statements>
ENDIF
For fans of the wildly varying world of programming languages note that ELSEIF and ENDIF are both one word.
It is possible to break out of loops by using the BREAK keyword e.g.
IF $x>0 AND $y>0
BREAK
ENDIF
this breaks out of the loop which immediately contains the BREAK keyword.
If the SQL contains a WHILE loop then a progress bar appears and you can break into the query. Obviously the progress bar does not actually progress, since it cannot work out how far into the running of the query you are.