The index on middleinitial is always worthless: a query that searches for one of the 26 possible values is faster if it just scans the entire table. The strftime () can take one or more modifiers. The index on givenname might be useful if you will do lookups on this column only. The order of transformation is from left to right. The index on surname is no longer needed because the three-column index can be used for any lookups on this column. JOIN fakenames_usa USING (givenname, middleinitial, surname) Ġ|1|0|SEARCH TABLE fakenames_uk USING COVERING INDEX uk_all_names (surname=? AND givenname=? AND middleinitial=?) To speed up this query, create this index permanently, so that it is no longer necessary to construct a temporary one: CREATE INDEX uk_all_names ON fakenames_uk(surname, givenname, middleinitial) The COUNT(*) operation does not need values from any other columns, so this index happens to be a covering index, which means that it is not necessary to actually look up the table row corresponding to an index entry, which saves even more I/O. This temporary ('AUTOMATIC') index is created on all colunms used for the search. This would be so bad that the database estimates that it is worthwhile to create and then drop a temporary index just for this query. If there is no index, the lookup of matching rows would require a complete table scan of the second table for each row of the first table. However, the middleinitial index is useless because it does not greatly reduce the number of table rows that need to be fetched and the additional step through the index actually increases the I/O needed because the table rows are no longer read in order, but randomly. Without any statistical information (which would be created by running ANALYZE), the database chooses the smallest one, to reduce I/O. In this case, there are three possible indexes. If there is an index, the database can look up any matches in the index quickly, and then go to the corresponding table row to get the values of any other columns that are needed. To establish a connection with SQLite3 database using python you need to Import the sqlite3 module using the import statement. In SQLite, joins are executed as nested loop joins, i.e., the database goes through one table, and for each row, searches matching rows from the other table. This is with indexes: 0|0|0|SCAN TABLE fakenames_ukĠ|1|1|SEARCH TABLE fakenames_usa USING INDEX idx_us_middleinitial (middleinitial=?) For more detailed information on the frame clause, check it out the window frame clause tutorial. The frameclause defines the subset (or the frame) of the current partition. Here's the result of EXPLAIN QUERY PLAN for the version without indexes: 0|0|0|SCAN TABLE fakenames_ukĠ|1|1|SEARCH TABLE fakenames_usa USING AUTOMATIC COVERING INDEX (middleinitial=? AND surname=? AND givenname=?) The ORDER BY clause sorts the rows in each partition to which the LASTVALUE() function applies. Then it runs painfully slowly: Downloads] $ time sqlite3 generic_data.sqlite 'select count(*) from fakenames_uk inner join fakenames_usa on fakenames_uk.givenname=fakenames_usa.givenname and fakenames_uk.surname=fakenames_usa.surname and fakenames_uk.middleinitial=fakenames_usa.middleinitial ' When there are no indexes except on the primary keys (irrelevant to this query), it runs quickly: Downloads] $ time sqlite3 generic_data_no_indexes.sqlite 'select count(*) from fakenames_uk inner join fakenames_usa on fakenames_uk.givenname=fakenames_usa.givenname and fakenames_uk.surname=fakenames_usa.surname and fakenames_uk.middleinitial=fakenames_usa.middleinitial 'īut if I add indexes to the three columns on each table (six indexes in all): CREATE INDEX `idx_uk_givenname` ON `fakenames_uk` (`givenname` ) I've constructed a simple query to find out how many names there are (given name, middle initial, surname) that are common to both tables: select count(*) from fakenames_uk inner join fakenames_usa on fakenames_uk.givenname=fakenames_usa.givenname and fakenames_uk.surname=fakenames_usa.surname and fakenames_uk.middleinitial=fakenames_usa.middleinitial I fixed this by moving the order_db() function inside of it after the select statement is executed.I have a sqlite database with two tables, each with 50,000 rows in, containing names of (fake) people. So my display_db() function was messing up and not showing them ordered. Or changing the format of the SQLite statement: (''' I have tried changing the function in different ways, using: cur.executemany(command) The function: # Orders database by high score The function I have made to do this runs fine, and produces no errors, but doesn't change the order in any way.Īm I doing something wrong? All help appreciated.

I'm trying to order all the records within by score in ascending order, so the highest score is at the top. I have a database containing the fields, username, password, scores, kills, and time.

Python sqlite order by