Online webcam muslims dating chat - Updating view

Now we want to write a query that finds out for which shoes currently in the store we have the matching shoelaces (color and length) and where the total number of exactly matching pairs is greater or equal to two.

SELECT shoe_ready.shoename, shoe_ready.sh_avail, shoe_ready.sl_name, shoe_ready.sl_avail, shoe_ready.total_avail FROM (SELECT rsh.shoename, rsh.sh_avail, rsl.sl_name, rsl.sl_avail, min(rsh.sh_avail, rsl.sl_avail) AS total_avail FROM shoe rsh, shoelace rsl WHERE rsl.sl_color = rsh.slcolor AND rsl.sl_len_cm SELECT shoe_ready.shoename, shoe_ready.sh_avail, shoe_ready.sl_name, shoe_ready.sl_avail, shoe_ready.total_avail FROM (SELECT rsh.shoename, rsh.sh_avail, rsl.sl_name, rsl.sl_avail, min(rsh.sh_avail, rsl.sl_avail) AS total_avail FROM (SELECT sh.shoename, sh.sh_avail, sh.slcolor, sh.slminlen, sh.slminlen * un.un_fact AS slminlen_cm, sh.slmaxlen, sh.slmaxlen * un.un_fact AS slmaxlen_cm, sh.slunit FROM shoe_data sh, unit un WHERE sh.slunit = un.un_name) rsh, (SELECT s.sl_name, s.sl_avail, s.sl_color, s.sl_len, s.sl_unit, s.sl_len * u.un_fact AS sl_len_cm FROM shoelace_data s, unit u WHERE s.sl_unit = u.un_name) rsl WHERE rsl.sl_color = rsh.slcolor AND rsl.sl_len_cm Two details of the query tree aren't touched in the description of view rules above.

These entries don't participate directly in the query, since they aren't referenced by the subquery's join tree or target list.

updating view-64

So the view is expanded as normal, but another unexpanded range-table entry is added to the query to represent the view in its capacity as the result relation.

The problem that now arises is how to identify the rows to be updated in the view.

The column names in an expanded column list are enclosed in quote marks to account for the possibility that the columns of the base object were originally entered with quotes and require them for the query to be syntactically correct.

As an example, assume that the statement, the database can create the view even if the defining query of the view cannot be executed.

Recall that when the result relation is a table, a special commands on a view.

These rules will rewrite the command, typically into a command that updates one or more tables, rather than views. Note that rules are evaluated first, rewriting the original query before it is planned and executed.

This is not such a simple example to start from and this makes things harder to get into.

But it's better to have one example that covers all the points discussed step by step rather than having many different ones that might mix up in mind.

For the example, we need a little CREATE TABLE shoe_data ( shoename text, -- primary key sh_avail integer, -- available number of pairs slcolor text, -- preferred shoelace color slminlen real, -- minimum shoelace length slmaxlen real, -- maximum shoelace length slunit text -- length unit ); CREATE TABLE shoelace_data ( sl_name text, -- primary key sl_avail integer, -- available number of pairs sl_color text, -- shoelace color sl_len real, -- shoelace length sl_unit text -- length unit ); CREATE TABLE unit ( un_name text, -- primary key un_fact real -- factor to transform to cm ); CREATE VIEW shoe AS SELECT sh.shoename, sh.sh_avail, sh.slcolor, sh.slminlen, sh.slminlen * un.un_fact AS slminlen_cm, sh.slmaxlen, sh.slmaxlen * un.un_fact AS slmaxlen_cm, sh.slunit FROM shoe_data sh, unit un WHERE sh.slunit = un.un_name; CREATE VIEW shoelace AS SELECT s.sl_name, s.sl_avail, s.sl_color, s.sl_len, s.sl_unit, s.sl_len * u.un_fact AS sl_len_cm FROM shoelace_data s, unit u WHERE s.sl_unit = u.un_name; CREATE VIEW shoe_ready AS SELECT rsh.shoename, rsh.sh_avail, rsl.sl_name, rsl.sl_avail, min(rsh.sh_avail, rsl.sl_avail) AS total_avail FROM shoe rsh, shoelace rsl WHERE rsl.sl_color = rsh.slcolor AND rsl.sl_len_cm INSERT INTO unit VALUES ('cm', 1.0); INSERT INTO unit VALUES ('m', 100.0); INSERT INTO unit VALUES ('inch', 2.54); INSERT INTO shoe_data VALUES ('sh1', 2, 'black', 70.0, 90.0, 'cm'); INSERT INTO shoe_data VALUES ('sh2', 0, 'black', 30.0, 40.0, 'inch'); INSERT INTO shoe_data VALUES ('sh3', 4, 'brown', 50.0, 65.0, 'cm'); INSERT INTO shoe_data VALUES ('sh4', 3, 'brown', 40.0, 50.0, 'inch'); INSERT INTO shoelace_data VALUES ('sl1', 5, 'black', 80.0, 'cm'); INSERT INTO shoelace_data VALUES ('sl2', 6, 'black', 100.0, 'cm'); INSERT INTO shoelace_data VALUES ('sl3', 0, 'black', 35.0 , 'inch'); INSERT INTO shoelace_data VALUES ('sl4', 8, 'black', 40.0 , 'inch'); INSERT INTO shoelace_data VALUES ('sl5', 4, 'brown', 1.0 , 'm'); INSERT INTO shoelace_data VALUES ('sl6', 0, 'brown', 0.9 , 'm'); INSERT INTO shoelace_data VALUES ('sl7', 7, 'brown', 60 , 'cm'); INSERT INTO shoelace_data VALUES ('sl8', 1, 'brown', 40 , 'inch'); SELECT * FROM shoelace; sl_name | sl_avail | sl_color | sl_len | sl_unit | sl_len_cm ----------- ---------- ---------- -------- --------- ----------- sl1 | 5 | black | 80 | cm | 80 sl2 | 6 | black | 100 | cm | 100 sl7 | 7 | brown | 60 | cm | 60 sl3 | 0 | black | 35 | inch | 88.9 sl4 | 8 | black | 40 | inch | 101.6 sl8 | 1 | brown | 40 | inch | 101.6 sl5 | 4 | brown | 1 | m | 100 sl6 | 0 | brown | 0.9 | m | 90 (8 rows) To expand the view, the rewriter simply creates a subquery range-table entry containing the rule's action query tree, and substitutes this range table entry for the original one that referenced the view.

The resulting rewritten query tree is almost the same as if you had typed: SELECT shoelace.sl_name, shoelace.sl_avail, shoelace.sl_color, shoelace.sl_len, shoelace.sl_unit, shoelace.sl_len_cm FROM (SELECT s.sl_name, s.sl_avail, s.sl_color, s.sl_len, s.sl_unit, s.sl_len * u.un_fact AS sl_len_cm FROM shoelace_data s, unit u WHERE s.sl_unit = u.un_name) shoelace;.

After you create a view, it appears in the Views list in the left pane.

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