Structured Query Language/Example Database Data< Structured Query Language
rDBMS offers different ways to put data into their storage: from csv files, Excel files, product specific binary files, via several API's or special gateways to other databases respectively database systems and some more technics. So there is a wide range of - non standardised - possibilities to bring data into our system. Because we are speaking about SQL we use the standardised INSERT command to do the job. It is available on all systems.
We use only a small amount of data because we want to keep things simple. Sometimes one needs a great number of rows to do performance tests. For this purpose we show a special INSERT command at the end of this page, which inflates your table in an exponential fashion.
-- -- After we have done a lot of tests we may want to reset the data to its original version. -- To do so use the DELETE command. But be aware of Foreign Keys: you may be forced to delete -- persons at the very end - with DELETE it's just the opposite sequence of tables in comparition to INSERTs. -- Be careful and don't confuse DELETE with DROP !! -- -- DELETE FROM person_hobby; -- DELETE FROM hobby; -- DELETE FROM contact; -- DELETE FROM person; -- COMMIT; INSERT INTO person VALUES (1, 'Larry', 'Goldstein', DATE'1970-11-20', 'Dallas', '078-05-1120', 95); INSERT INTO person VALUES (2, 'Tom', 'Burton', DATE'1977-01-22', 'Birmingham', '078-05-1121', 75); INSERT INTO person VALUES (3, 'Lisa', 'Hamilton', DATE'1975-12-23', 'Richland', '078-05-1122', 56); INSERT INTO person VALUES (4, 'Kim', 'Goldstein', DATE'2011-06-01', 'Shanghai', '078-05-1123', 11); INSERT INTO person VALUES (5, 'James', 'de Winter', DATE'1975-12-23', 'San Francisco', '078-05-1124', 75); INSERT INTO person VALUES (6, 'Elias', 'Baker', DATE'1939-10-03', 'San Francisco', '078-05-1125', 55); INSERT INTO person VALUES (7, 'Yorgos', 'Stefanos', DATE'1975-12-23', 'Athens', '078-05-1126', 64); INSERT INTO person VALUES (8, 'John', 'de Winter', DATE'1977-01-22', 'San Francisco', '078-05-1127', 77); INSERT INTO person VALUES (9, 'Richie', 'Rich', DATE'1975-12-23', 'Richland', '078-05-1128', 90); INSERT INTO person VALUES (10, 'Victor', 'de Winter', DATE'1979-02-28', 'San Francisco', '078-05-1129', 78); COMMIT;
-- DELETE FROM contact; -- COMMIT; INSERT INTO contact VALUES (1, 1, 'fixed line', '555-0100'); INSERT INTO contact VALUES (2, 1, 'email', 'email@example.com'); INSERT INTO contact VALUES (3, 1, 'email', 'lg@my_company.xx'); INSERT INTO contact VALUES (4, 1, 'icq', '12111'); INSERT INTO contact VALUES (5, 4, 'fixed line', '5550101'); INSERT INTO contact VALUES (6, 4, 'mobile', '10123444444'); INSERT INTO contact VALUES (7, 5, 'email', 'firstname.lastname@example.org'); INSERT INTO contact VALUES (8, 7, 'fixed line', '+30000000000000'); INSERT INTO contact VALUES (9, 7, 'mobile', '+30695100000000'); COMMIT;
-- DELETE FROM hobby; -- COMMIT; INSERT INTO hobby VALUES (1, 'Painting', 'Applying paint, pigment, color or other medium to a surface.'); INSERT INTO hobby VALUES (2, 'Fishing', 'Catching fishes.'); INSERT INTO hobby VALUES (3, 'Underwater Diving', 'Going underwater with or without breathing apparatus (scuba diving / breath-holding).'); INSERT INTO hobby VALUES (4, 'Chess', 'Two players have 16 figures each. They move them on an eight-by-eight grid according to special rules.'); INSERT INTO hobby VALUES (5, 'Literature', 'Reading books.'); INSERT INTO hobby VALUES (6, 'Yoga', 'A physical, mental, and spiritual practices which originated in ancient India.'); INSERT INTO hobby VALUES (7, 'Stamp collecting', 'Collecting of post stamps and related objects.'); INSERT INTO hobby VALUES (8, 'Astronomy', 'Observing astronomical objects such as moons, planets, stars, nebulae, and galaxies.'); INSERT INTO hobby VALUES (9, 'Microscopy', 'Observing very small objects using a microscope.'); COMMIT;
-- DELETE FROM person_hobby; -- COMMIT; INSERT INTO person_hobby VALUES (1, 1, 1); INSERT INTO person_hobby VALUES (2, 1, 4); INSERT INTO person_hobby VALUES (3, 1, 5); INSERT INTO person_hobby VALUES (4, 5, 2); INSERT INTO person_hobby VALUES (5, 5, 3); INSERT INTO person_hobby VALUES (6, 7, 8); INSERT INTO person_hobby VALUES (7, 4, 4); INSERT INTO person_hobby VALUES (8, 9, 8); INSERT INTO person_hobby VALUES (9, 9, 9); COMMIT;
For realistic performance tests we need a huge amount of data. The few number of rows in our example database does not meet this criteria. How can we generate test data and store it in a table? There are different possibilities: FOR loops in a procedure, (pseudo-) recursive calls, importing external data in a system specific fashion and some more.
Because we are dealing with SQL we introduce an INSERT command which is portable across all rDBMS. Although it has a simple syntax it is very powerful. With every execution it will double the number of rows. Suppose there is 1 row in a table. After the first execution there will be a second row in the table. At first glance this sounds boring. But after 10 executions there are more than thousand rows, after 20 executions there are more than a million, and we suspect that only few installations are able to execute it more than 30 times.
INSERT INTO person (id, firstname, lastname, weight) SELECT id + (select max(id) from person), firstname, lastname, weight FROM person; COMMIT;
The command is an INSERT in combination with a (Sub-)SELECT. The SELECT retrievs all rows of the table because there is no WHERE clause. This is the reason for the doubling. The mandatory columns firstname and lastname keeps unchanged. We ignore optional columns. Only the primary key id is computed. The new value is the sum of the old value plus the highest available id when starting the command.
Some more remarks:
- max(id) is determined only once per execution! This illustrates an important aspect of rDBMS: At a conceptual level the database has a certain state before execution of a command and a new state after its execution. Commands are atomic operations moving the database from one state to another - they run completely or not a bit! Both, the SELECT and the inner SELECT with the max(id), act on the initial state. They never see the result or an intermediate result of the INSERT. Otherwise the INSERT would never end.
- If we wish to observe the process of growing, we can add a column to the table to store max(id) with each iteration.
- The computation of the new id may be omitted if the DBMS supports AUTO INCREMENT columns.
- For performance tests it may be helpful to store some random data in one or more columns.