我坚持使用SQL查询，其想法是我有一个数据库，我将所有文档与每个文档version(revisionNumber)等一起保存。我要实现的目标是，我目前只想访问那些文档中包含最新的revisionNumber。
| id | title | documentForm | revisionNumber | effectiveDate |
| --: | ------------------- | -------------| -------------: | :------------ |
| 1 | Event Calendar | SOP-CL | 1.0 | 2011-02-02 |
| 2 | Event Calendar | SOP-CL | 2.0 | 2012-12-16 |
| 3 | Event Calendar | SOP-CL | 3.0 | 2014-02-15 |
| 4 | Event Calendar | SOP-CL | 4.0 | 2014-08-01 |
| 5 | Event Calendar | SOP-CL | 5.0 | 2016-09-12 |
| 6 | Event Calendar | SOP-CL | 6.0 | 2018-09-11 |
| 7 | Software development| SOP-DEV | 1.0 | 2015-11-25 |
| 8 | Granting and... | SOP-GRA | 1.0 | 2014-08-04 |
| 9 | Granting and... | SOP-GRA | 2.0 | 2015-12-07 |
| 10 | Granting and... | SOP-GRA | 3.0 | 2018-03-26 |
在这里您可以看到查询后我需要获得的结果：
| id | title | documentForm | revisionNumber | effectiveDate |
| --: | ------------------- | ------------ | -------------: | :------------ |
| 6 | Event Calendar | SOP-CL | 6.0 | 2018-09-11 |
| 7 | Software development| SOP-CL | 1.0 | 2015-11-25 |
| 3 | Granting and... | SOP-GRA | 3.0 | 2018-03-26 |
我一直在Google中进行搜索，发现可以通过对文档进行分组（例如-documentForm）并返回MAX(revisionNumber)来完成，但是我没有得到正确的行id和{{1} }。我想我只是不正确地使用它们。
答案 0 :(得分：2)
使用相关子查询
arc答案 1 :(得分：2)
您可以尝试在where子句中使用子查询。
模式（MySQL v5.6）
CREATE TABLE t (
title varchar(50),
documentForm varchar(50),
effectiveDate date,
revisionNumber int
);
insert into t values ('vent Calendar','SOP-CL','2011-02-02',1.0);
insert into t values ('vent Calendar','SOP-CL','2012-12-16',2.0);
insert into t values ('vent Calendar','SOP-CL','2014-02-15',3.0);
insert into t values ('vent Calendar','SOP-CL','2014-08-01',4.0);
insert into t values ('vent Calendar','SOP-CL','2016-09-12',5.0);
insert into t values ('vent Calendar','SOP-CL','2018-09-11',6.0);
insert into t values ('oftware development ','SOP-DEV','2015-11-25',1.0);
insert into t values ('ranting and..','SOP-GRA','2014-08-04',1.0);
insert into t values ('ranting and..','SOP-GRA','2015-12-07',2.0);
insert into t values ('ranting and..','SOP-GRA','2018-03-26',3.0);
查询＃1
SELECT *
FROM t t1
WHERE revisionNumber = (
select max(tt.revisionNumber)
from t tt
WHERE t1.documentForm = tt.documentForm
);
| title | documentForm | effectiveDate | revisionNumber |
| -------------------- | ------------ | ------------- | -------------- |
| vent Calendar | SOP-CL | 2018-09-11 | 6 |
| oftware development | SOP-DEV | 2015-11-25 | 1 |
| ranting and.. | SOP-GRA | 2018-03-26 | 3 |
答案 2 :(得分：1)
具有一个子查询，该查询执行function discount_table(){
$cat_in_cart = false;
$tot_cat = 0;
foreach ( WC()->cart->get_cart() as $cart_item ) {
if ( has_term( 'cat1', 'product_cat', $cart_item['product_id'] ) ) {
$cat_in_cart = true;
$tot_cat_price = $cart_item['data']->get_price();
$tot_cat_qty = $cart_item['quantity'];
$tot_cat += $tot_cat_price * $tot_cat_qty;
//break;
/* commented here, thanks to Michael Ramin: break will stop execution of the loop after found the first product belonging to the category; what if you have more than one? so remove break instruction */
}
}
global $product;
$total = WC()->cart->subtotal;
$discount_label = "";
if($total >= 300){
$discount_label=15;
}elseif($total >= 220){
$discount_label=10;
}elseif($total >= 150){
$discount_label=8;
}elseif($total >= 100){
$discount_label=4;
}
$chosen_methods = WC()->session->get( 'chosen_shipping_methods' );
$chosen_shipping = explode(':',$chosen_methods[0]);
if($chosen_shipping[0]=='local_pickup'){
$discount_label=25;
}
$discount_brand = ($total-$tot_cat)*$discount_label/100;
if($discount_label!=""){
$discount_brand_net = ($discount_brand/1.1);
if($discount_brand_net != 0) // show discount only if != 0; it may happen if cart includes only targeted category products;
WC()->cart->add_fee( "Discount ($discount_label%)", -$discount_brand_net, false );
}
}
add_action( 'woocommerce_cart_calculate_fees','discount_table' );
返回具有最高修订版本号的每个documentForm。 GROUP BY得到的结果：
JOIN