Merge trunk enhancements into the pushdown-subquery branch.

FossilOrigin-Name: 27865e316f8dfbf4c20290cf1be3024d7518fec46655e34f3fc435e15346c63e

1 files changed, 6 insertions, 0 deletions

diff --git a/src/wherecode.c b/src/wherecode.c
index 47ce36ce3..1f9c84f00 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -2474,6 +2474,12 @@ Bitmask sqlite3WhereCodeOneLoopStart(
   ** iLoop==3: Code all remaining expressions.
   **
   ** An effort is made to skip unnecessary iterations of the loop.
+  **
+  ** This optimization of causing simple query restrictions to occur before
+  ** more complex one is call the "push-down" optimization in MySQL.  Here
+  ** in SQLite, the name is "MySQL push-down", since there is also another
+  ** totally unrelated optimization called "WHERE-clause push-down".
+  ** Sometimes the qualifier is omitted, resulting in an ambiguity, so beware.
   */
   iLoop = (pIdx ? 1 : 2);
   do{