Check for more subquery rules and subquery types. More examples of Nested Subqueries. IN / NOT IN – This operator takes the output of the inner query after the inner query gets executed which can be zero or more values and sends it to the outer query. The outer query then fetches all the matching [IN operator] or non matching [NOT IN operator ...
The use of CTEs or derived tables (in MS SQL at least) can be useful to format a SQL statement without splitting it into separate queries using temp tables to "join" them.
Which of these queries is the faster? NOT EXISTS: SELECT ProductID, ProductName FROM Northwind..Products p WHERE NOT EXISTS ( SELECT 1 FROM Northwind..[Order Details] od WHERE p.
Since I need to test some of those queries in detail, how can I write the query in management studio? I want to write the query with parameters and give a value to the parameter.
Why write your SQL like that? Decompose your queries, just like you decompose your functions. This makes them shorter, simpler, easier to comprehend, easier to test, easier to refactor. And it allows you to add "shims" between them, and "wrappers" around them, just as you do in procedural code. How do you do this?
In SQL, an ad hoc query is a loosely typed command/query whose value depends upon some variable. Each time the command is executed, the result is different, depending on the value of the variable. It cannot be predetermined and usually comes under dynamic programming SQL query. An ad hoc query is short lived and is created at runtime.
I've heard that "everyone" is using parameterized SQL queries to protect against SQL injection attacks without having to vailidate every piece of user input. How do you do this? Do you get this
4 Personally I prefer to avoid nested queries until they are necessary for the simple reason that nested queries can make the code less human readable and make debugging and collaboration more painful. I think nesting is acceptable if the nested query is something trivial or if temporary storage of large tables becomes an issue.
15 Since you've already received help on the query, I'll take a poke at your syntax question: The first query employs some lesser-known ANSI SQL syntax which allows you to nest joins between the join and on clauses. This allows you to scope/tier your joins and probably opens up a host of other evil, arcane things.
The examples in antlr need a lot of work to convert to a nice ast in python. The sql standard grammars are here, but it would be a full time job to convert them yourself and it is likely that you would only need a subset of them i.e no joins.
