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SqlExp and LIMIT [message #2933]

Sun, 30 April 2006 22:58

mezise
Messages: 54
Registered: April 2006

Member

Code from reference/SQL_Sqlite3/simple.cpp:

	// Test selection:
	sql*Select(row).From(SIMPLE_TEST1);

How to apply "LIMIT 15" clause?

There is not something like this:

	// Test selection:
	sql*Select(row).From(SIMPLE_TEST1).Limit(15);

Michal

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Re: SqlExp and LIMIT [message #2934 is a reply to message #2933]

Sun, 30 April 2006 23:01

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

mezise wrote on Sun, 30 April 2006 16:58

Code from reference/SQL_Sqlite3/simple.cpp:

	// Test selection:
	sql*Select(row).From(SIMPLE_TEST1);

How to apply "LIMIT 15" clause?

There is not something like this:

	// Test selection:
	sql*Select(row).From(SIMPLE_TEST1).Limit(15);

Michal

Not yet. To put it straight, so far SqlExp was designed for Oracle and will need further tweaks for other SQL engines.

Mirek

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Re: SqlExp and LIMIT [message #2941 is a reply to message #2934]

Mon, 01 May 2006 03:06

mezise
Messages: 54
Registered: April 2006

Member

luzr wrote on Sun, 30 April 2006 17:01

Not yet. To put it straight, so far SqlExp was designed for Oracle and will need further tweaks for other SQL engines.

Mirek

OFFSET-LIMIT clause is quite necessary in MySQL, SQLite and PostgreSQL.
So, could this code be put into next dev5 release?

into Sqlexp.h:

	SqlSet&          Limit(const unsigned int limit);
	SqlSet&          Limit(const unsigned int offset, const unsigned int limit);
	SqlSet&          Offset(const unsigned int offset);

into Sqlexp.cpp:

SqlSet& SqlSet::Limit(const unsigned int limit) {
	text << " limit " << limit;
	return *this;
}

SqlSet& SqlSet::Limit(const unsigned int offset, const unsigned int limit) {
	text << " limit " << offset << ", " << limit;
	return *this;
}

SqlSet& SqlSet::Offset(const unsigned int offset) {
	text << " offset " << offset;
	return *this;
}

After OrderBy it would be the right place.

Michal

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Re: SqlExp and LIMIT [message #2943 is a reply to message #2941]

Mon, 01 May 2006 09:58

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

mezise wrote on Sun, 30 April 2006 21:06

luzr wrote on Sun, 30 April 2006 17:01

Not yet. To put it straight, so far SqlExp was designed for Oracle and will need further tweaks for other SQL engines.

Mirek

OFFSET-LIMIT clause is quite necessary in MySQL, SQLite and PostgreSQL.
So, could this code be put into next dev5 release?

Definitely! Done. Thank you, that is the kind of response I like Wink

BTW, speaking about it, you should be aware of Sql refactoring plan....

The problem there now is with dialects AND using multiple engines at once (like Oracle and MySql in single app).

There are two problems - SQL dialects differ AND of course, "implicit session" are now two...

Well, several month ago plan was to bind the dialect with "execution" Sql - that would involve storing SqlExp into some intermediate language form and then "compiling" it for target engine. Also, implicit session and default SQL cursor (which in fact are related) would be gone in multisession apps.

However, further thinking revealed that it would still be difficult to use - you would have to quote session when makeing any Sql cursor. So the current plan, somewhat less elegant but I believe more productive, is simply to have per-thread "current session" variable and change it using RAII push/pops, something like

void MyFn() {
UseSqlSession __(MySqlSession);
// now until __ destructor, MySqlSession and MySQL dialect are used for everything, SQL reffers to MySqlSession
}

maybe, using macro hackery, we could also introduce form

void MyFn() {
SQLCONTEXT(MySqlSession) {
.....
}
}

That also means that those "dialect" members of SqlS are likely to be gone in favor of single per-thread global variable.

Mirek

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