If you build a query dynamically with rejoin or something, the query is put together client side and then the server has to generate a new query plan for each distinct set of parameter values. This takes time and blows the query plan cache, which slows down the whole query process.
The problem is that your ad-hoc parameter screening is usually not perfect. Parameterized queries don't build a query in the server, they just plug in the values to an already-compiled query (the "query plan"). The server doesn't have to do any parameter screening other than for malformed values in the protocol.
TomBon
depends on the needs. I always try to detach the data sink from input logic. this way you can change your db backend very easy but of course everybody has it's own style in this.
BrianH
For new developers ad-hoc parameter screening is even more likely to be bad (and most that don't use parameterized queries are still new, no matter how long they've been programming, because parameterized queries are almost always inherently better). Even if it wasn't a safety issue, they're a lot faster.
I've seen data front-ends that don't use parametrized queries when talking to SQL servers that support them. They need work.
afsanehsamim
could you tell me how can i compare values of two tables in database?
Endo
About parametrized queries: The only problem using them on R2, at least with RT's default ODBC, there is no chance to use NULL values. None of those work: insert db-port ["INSERT t (a) VALUES (?)" NULL] insert db-port ["INSERT t (a) VALUES (?)" 'NULL] insert db-port ["INSERT t (a) VALUES (?)" "NULL"] insert db-port ["INSERT t (a) VALUES (?)" none] insert db-port reduce ["INSERT t (a) VALUES (?)" none]
TomBon
you have more than one solution, the first is a simple serial SELECT on each table -> compare the output for equal. of course this produce unnecessary DB overhead but I guess you won't feel any speed difference except you are serving a whole city concurrently. another, better one is a JOIN or UNION.
SELECT table_name1.column_name(s), ... FROM table_name1 LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name
the JOIN direction (LEFT,RIGHT,INNER) for your reference table is important here. the resultset is a table containing BOTH columns. if both having a value -> match, if one is empty then you don't.
index both fields to accelerate the query and use something like the free SQLyog to test different queries to make debugging easier for you.
while you situation reminds me to myself, sitting infront of a monochrom asthon tate dot some decades ago and asking what next?, you should 'bite' yourself now thru the rest. It won't help you on longterm if you don't.
afsanehsamim
@TomBon: my query for joining two tables is :insert db["select * from data LEFT JOIN data1 ON data.oneone=data1.oneone"] and output is :[ ["c" "a" "t" "a" "e" "r" "o" "a" none none none none none none none none] ] plz tell me what should i write in query that i get values instead of none in output ?
afsanehsamim
guys when i enter correct value in form the above join query works properly... i need help for writing queries which other condition,it means if user enter wrong value ,it joins with first table but dose comparing indicidually and shows error message.
the output of this query insert db[{select * from data LEFT JOIN data1 ON data.oneone=data1.oneone}] is : [ ["c" "a" "t" "a" "e" "r" "o" "a" "c" "a" "t" "a" "e" "r" "o" "a"] ]