Evaluation of nested IF in MySQL - mysql

Question

I found this code in a WordPress plugin, but I cannot understand what does it mean or how it can be read.
Can somebody to help me underdstaint this code :?
IF(agr_sam_ads.ad_users = 0, TRUE, IF(agr_sam_ads.ad_users_reg = 1, IF(agr_sam_ads.x_ad_users = 1, NOT FIND_IN_SET("admin", agr_sam_ads.x_view_users), TRUE ....
I have not paste the whole query because it is huge. In what I am interested to be helped is the part of the Query that looks like that:
IF(expression, value, IF(expression, IF(expression, SQL Logical Query, value ...
I have not see this syntax, and I don't know where to search for that. In MySQL documentation the IF statement syntax is like that : http://dev.mysql.com/doc/refman/5.0/en/if.html and it is not looks like the one I have paste above.
Just for the users are interested in the full code, the code is here:
SELECT
agr_sam_places.id,
agr_sam_places.name,
agr_sam_places.description,
agr_sam_places.code_before,
agr_sam_places.code_after,
agr_sam_places.place_size,
agr_sam_places.place_custom_width,
agr_sam_places.place_custom_height,
agr_sam_places.patch_img,
agr_sam_places.patch_link,
agr_sam_places.patch_code,
agr_sam_places.patch_adserver,
agr_sam_places.patch_dfp,
agr_sam_places.patch_source,
agr_sam_places.trash,
(
SELECT
COUNT(*)
FROM
agr_sam_ads
WHERE
agr_sam_ads.pid = agr_sam_places.id
AND
agr_sam_ads.trash IS FALSE
) AS ad_count,
(
SELECT
COUNT(*)
FROM
agr_sam_ads
WHERE
agr_sam_ads.pid = agr_sam_places.id
AND
agr_sam_ads.trash IS FALSE
AND
(
IF(agr_sam_ads.ad_users = 0, TRUE, IF(agr_sam_ads.ad_users_reg = 1, IF(agr_sam_ads.x_ad_users = 1, NOT FIND_IN_SET("admin", agr_sam_ads.x_view_users), TRUE
)
AND
IF(agr_sam_ads.ad_users_adv = 1, (agr_sam_ads.adv_nick <> "admin"), TRUE), FALSE)))
AND
(
(
agr_sam_ads.view_type = 1
)
OR
(
agr_sam_ads.view_type = 0
AND
(
agr_sam_ads.view_pages+0 & 256
)
)
)
AND
(
agr_sam_ads.ad_cats = 0
)
AND
(
agr_sam_ads.ad_authors = 0
)
AND
IF(agr_sam_ads.ad_schedule, CURDATE() BETWEEN agr_sam_ads.ad_start_date AND agr_sam_ads.ad_end_date, TRUE)
AND
IF(agr_sam_ads.limit_hits, agr_sam_ads.hits_limit > agr_sam_ads.ad_hits, TRUE)
AND
IF(agr_sam_ads.limit_clicks, agr_sam_ads.clicks_limit > agr_sam_ads.ad_clicks, TRUE)
AND
(
agr_sam_ads.ad_weight > 0
)
) AS ad_logic_count,
(
SELECT
COUNT(*)
FROM
agr_sam_ads
WHERE
agr_sam_ads.pid = agr_sam_places.id
AND
agr_sam_ads.trash IS FALSE
AND
(
IF(agr_sam_ads.ad_users = 0, TRUE, IF(agr_sam_ads.ad_users_reg = 1, IF(agr_sam_ads.x_ad_users = 1, NOT FIND_IN_SET("admin", agr_sam_ads.x_view_users), TRUE)
AND
IF(agr_sam_ads.ad_users_adv = 1, (agr_sam_ads.adv_nick <> "admin"), TRUE), FALSE)))
AND
(
(
agr_sam_ads.view_type = 1
)
OR
(
agr_sam_ads.view_type = 0
AND
(
agr_sam_ads.view_pages+0 & 256
)
)
)
AND
(
agr_sam_ads.ad_cats = 0
)
AND
(
agr_sam_ads.ad_authors = 0
)
AND
IF(agr_sam_ads.ad_schedule, CURDATE() BETWEEN agr_sam_ads.ad_start_date AND agr_sam_ads.ad_end_date, TRUE)
AND
IF(agr_sam_ads.limit_hits, agr_sam_ads.hits_limit > agr_sam_ads.ad_hits, TRUE)
AND
IF(agr_sam_ads.limit_clicks, agr_sam_ads.clicks_limit > agr_sam_ads.ad_clicks, TRUE)
AND
IF(agr_sam_ads.ad_weight > 0, (agr_sam_ads.ad_weight_hits*10/(agr_sam_ads.ad_weight*1000)) < 1, FALSE)
) AS ad_full_count
FROM
agr_sam_places
WHERE
agr_sam_places.id = 10
AND
agr_sam_places.trash IS FALSE;

Answer 1

It should be read as:
IF (
expression,
valueIfExpressionIsTrue,
valueIfExpressionIsValue
)
So to take part of your code:
IF(
agr_sam_ads.ad_users = 0,
TRUE,
IF(
agr_sam_ads.ad_users_reg = 1,
2,
3
)
)
I see that you're familiar with PHP, so essentially if this was PHP, the code would be
if ($arg_sam_ads_ad_users == 0) {
return true;
} else {
if ($arg_sam_ads_ad_users_reg == 1) {
return 2;
} else {
return 3;
}
}

Answer 2

This is basically creating an IF-ELSE tree without using the IF _ THEN _ ELSE _ ENDIF syntax.
Take the following example:
IF(1=0, 1, IF(1=1, 1, 0))
This is the equivalent of the following with C syntax:
IF (1=0) {
1
}
ELSE IF (1=1) {
1
}
ELSE {
0
}
The more common SQL syntax is the following:
IF 1=0 THEN
1;
ELSEIF 1=1 THEN
1;
ELSE
0;
ENDIF;