On 28 May 2014, at 3:55pm, Drago, William @ MWG - NARDAEAST <william.dr...@l-3com.com> wrote:
> Can someone tell me what an appropriate use for REPLACE is? REPLACE in SQlite is just a way of writing INSERT OR REPLACE ... It's best use is when you are not sure whether a record already exists or not. And the definition of 'exists' is that the new row has data which clashes with an existing row by at least one UNIQUE constraint, including the rule that primary keys must be UNIQUE. So an example is if you have a big table of equipment, and a smaller table listing all equipment which is on loan. One row for each item on loan, and everything not mentioned in this smaller table should be in the stock room. The smaller table would have a UNIQUE key on the equipment number to prevent it from listing one item being on loan to two different people. If you discover that item number 515 is on loan to Barry now you need to make sure that Barry is listed in that table. But you don't know whether you're creating a new row or replacing a row that said that the equipment was on loan to Amanda last week. So you use INSERT OR REPLACE and SQLite works out whether it has to delete an existing row before it can insert the new one. Simon. _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
