where-clause

问题 how would you do a mysql query where a user can choose from multiple options. Fox example I have a form that user can use to search for houses. Now I have a select box where you can chosse whether you want a house, a flat or whatever. Then I have a second box where you can choose for example the city you want the house or flat to be in. And maybe another one with the maximum price. Now how would you do the mysql query? My problem is, I would do it like that: if($_POST["house_type"] != 0) {

问题 I have a table with many (maybe more than 500) different attributs in an "attribut"-column and wanted to find the rows, which contans many certan attributs (~ 200). The query to find them would contain a huge number of where-clauses. How many where-clauses is okay, to have an acceptable performance? 回答1: It's not the quantity that matters. It's how well you've designed your database structure and query that matter. Make sure you have an index on the columns that will be used in your where

问题 I have started to use JSqlParser, i can parse a Where clause but i don't manage to go further with it. JSqlParser github link Indeed, i have tried to Override visit methods but don't understand how to reach my goal. Let's say i have: (a=1 AND (b=2 OR (c=3 AND d=4))) OR e=2 as input and i would like as output: -> a=1 -> AND --> b=2 --> OR ---> c=3 ---> AND ---> d=4 -> OR -> e=5 My final goal is not a pretty print, but to understand how to know the current depth of the print at a given state.

问题 I know I can use CASE statement in an SQLite query but I don't know how to built it in a WHERE clause. Actually I have this in a long WHERE clause (this is just the part concerned by the question): AND (%d >= (wines.year + wines.maturity)) AND (%d < (wines.year + wines.apogee)) In fact I want just that : AND (%d >= (wines.year + wines.maturity)) => if wines.apogee IS NULL or also: AND (%d >= (wines.year + wines.maturity)) AND (%d < (wines.year + wines.apogee)) => if wines.apogee IS NOT NULL

问题 I am new to SQL and doing the learning via datacamp. I was wondering if you can achieve the same result with 'HAVING' as with a nested 'WHERE' clause. Related: SQL - having VS where I understand that HAVING is used with aggregate functions such as min, max, .. How could I rewrite the following with HAVING?: SELECT * FROM populations WHERE year = 2015 AND life_expectancy >( SELECT AVG(life_expectancy)*1.15 FROM populations ); Suppose I have 6 columns in the table 'populations': A (character),

问题 I am trying to retrieve document id's over a one-to-many table. I want to use a List in the where clause to find all id's that are connected with every element in the list. List<int> docIds = (from d in doc where _tags.Contains(d.Tags) select d.id).ToList<int>(); I know that the contains must be incorrect but I can't work it out. If I try a foreach I can't work out how to check if the document contains all Tags. 回答1: If you want that all d.Tags should be in the included in the _tags list, you

问题 I wrote the following function to sum over an iterator: use std::ops::Add; fn sum_iter<I>(s: I, init: &I::Item) -> I::Item where I: Iterator + Clone, <I as Iterator>::Item: Add<I::Item, Output = I::Item> + Copy, { s.clone().fold(*init, |acc, item| acc + item) } This compiles fine with Rust 1.0.0, but it would be nice if one could avoid repeating I::Item four times and instead refer to a type T and say somewhere that Iterator::Item = T only once. What's the right way to do this? 回答1: You can

问题 I'd like to select posts that have one or more comments using Rails 3 and a single query. I'm trying something like this: Post.includes(:comments).where('count(comments.id)>0') However I get this error: ActiveRecord::StatementInvalid: PGError: ERROR: aggregates not allowed in WHERE clause I've googled this and similar approaches, group by, etc with no luck. Any help will be appreciated. 回答1: I'm sure you may have figured this out by now, but I believe what you're looking for is the having(

问题 In what order would this be evaluated. My intension is that if it finds either foo or bar, it would also search for lol and rofl. Is this totally in the woods? And if so, how would one evaluate an expression like that. 回答1: The AND operator has higher precedence than OR in MySql, so your current expression evaluates as: WHERE 'foo' OR ('bar' AND 'lol') OR 'rofl' Add parentheses to the expression if you want to force the evaluation order: WHERE ('foo' OR 'bar') AND ('lol' OR 'rofl') 回答2: AND

问题 I've got a table that returns the history of a value, as well as the current one, each with a date. The oldest date is the main record. If the value is changed, a new record is created, with the old value, and the main record is updated with the new value. If this happens again, a third record is created, which contains the now old value. So if the value starts at 4, changes to 2, then again changes to 1. The records will go 1 4 2 I'm currently creating an inner join on the table to itself as