Hy all!
Could someone help me to understand the meaning?
This is the structure of sql string:
---------------------
SELECT *
FROM table_1, table_2
WHERE
field_1.table_1 = "x"
AND
field_1.table_2 = field_2.table_1
AND
field_2.table_2 = "y"
AND
field_3.table_1 = "z"
---------------------
now, this structure find for occurrences as the first statement of WHERE
(field_1.table_1 = "x")
was absent
so it searches and find as I wrote:
---------------------
SELECT *
FROM table_1, table_2
WHERE
field_1.table_2 = field_2.table_1
AND
field_2.table_2 = "y"
AND
field_3.table_1 = "z"
---------------------
the same if I put the last statement at beginning substituting that one.
BUT
if I put statement searching for x and z at beginning as in :
SELECT *
FROM table_1, table_2
WHERE
field_1.table_1 = "x"
AND
field_3.table_1 = "z"
AND
field_1.table_2 = field_2.table_1
AND
field_2.table_2 = "y"
alla works fine!
-----
FINALLY if the sequence is
SELECT *
FROM table_1, table_2
WHERE
field_1.table_2 = field_2.table_1
AND
field_2.table_2 = "y"
AND
field_1.table_1 = "x"
AND
field_3.table_1 = "z"
it will search and find as the last query didn't exist. alias it considers
anly the first statement after searching in table_2
What's the rule?
THANKS!
©2002 Luca Porfiri |
