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Speed up removing of comments from SQL queries

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This commit replaces the regular expressions for removing end of line
and block comments from SQL queries provided by the user by a hand
written state machine. This makes the code a lot faster, especially for
longer SQL scripts with many statements and many comments in them. It is
also not harder to read than the rather complex regular expressions from
before - possibly even easier to read.

See issue #2619.
This commit is contained in:
Martin Kleusberg
2021-03-15 19:38:36 +01:00
parent a5cc259b45
commit ccb8c9ee97
1 changed files with 35 additions and 43 deletions
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78
src/sqlitetablemodel.cpp
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@@ -719,58 +719,50 @@ void SqliteTableModel::updateAndRunQuery()
void SqliteTableModel::removeCommentsFromQuery(QString& query)
{
// Store the current size so we can easily check later if the string has been changed
int oldSize = query.size();
// first remove block comments
// This implements a simple state machine to strip the query from comments
QChar quote;
for(int i=0;i<query.size();i++)
{
QRegExp rxSQL("^((?:(?:[^'/]|/(?![*]))*|'[^']*')*)(/[*](?:[^*]|[*](?!/))*[*]/)(.*)$"); // set up regex to find block comment
QString result;
while(query.size() != 0)
// Are we in quote state?
if(quote.isNull())
{
int pos = rxSQL.indexIn(query);
if(pos > -1)
// We are currently not in quote state
// So are we starting a quote?
if((query.at(i) == '\'' || query.at(i) == '\"' || query.at(i) == '[') && (i == 0 || query.at(i-1) != '\\'))
{
result += rxSQL.cap(1) + " ";
query = rxSQL.cap(3);
} else {
result += query;
query.clear();
// Quoted text is beginning. Switch to the quote state
quote = query.at(i);
} else if(query.at(i) == '-' && i+1 < query.size() && query.at(i+1) == '-') {
// This is an end of line comment. Remove anything till the end of the line or the end of the string if this is the last line
int pos_next_line_break = query.indexOf('\n', i);
if(pos_next_line_break == -1)
query = query.left(i);
else
query.remove(i, pos_next_line_break - i); // The \n is left in intentionally
} else if(query.at(i) == '/' && i+1 < query.size() && query.at(i+1) == '*') {
// This is a block comment. Remove anything till the end of the block or the end of the string if the block is not closed
int pos_end_comment = query.indexOf("*/", i);
if(pos_end_comment == -1)
query = query.left(i);
else
query.remove(i, pos_end_comment - i + 2); // Add 2 to include the */
}
} else {
// We are currently in quote state
// If this is the closing quote character, switch back to normal state
if((query.at(i) == quote) && (i == 0 || query.at(i-1) != '\\'))
quote = 0;
}
query = result;
}
// deal with end-of-line comments
{
/* The regular expression for removing end of line comments works like this:
* ^((?:(?:[^'-]|-(?!-))*|(?:'[^']*'))*)(--.*)$
* ^ $ # anchor beginning and end of string so we use it all
* ( )( ) # two separate capture groups for code and comment
* --.* # comment starts with -- and consumes everything afterwards
* (?: | )* # code is none or many strings alternating with non-strings
* (?:'[^']*') # a string is a quote, followed by none or more non-quotes, followed by a quote
* (?:[^'-]|-(?!-))* # non-string is a sequence of characters which aren't quotes or hyphens,
*/
QRegExp rxSQL("^((?:(?:[^'-]|-(?!-))*|(?:'[^']*'))*)(--[^\\r\\n]*)([\\r\\n]*)(.*)$"); // set up regex to find end-of-line comment
QString result;
while(query.size() != 0)
{
int pos = rxSQL.indexIn(query);
if(pos > -1)
{
result += rxSQL.cap(1) + rxSQL.cap(3);
query = rxSQL.cap(4);
} else {
result += query;
query.clear();
}
}
query = result.trimmed();
}
query = query.trimmed();
if (oldSize != query.size()) {
// Remove multiple line breaks that might have been created by deleting comments till the end of the line but not including the line break