On Sat, Apr 1, 2017 at 2:01 PM, Richard Hipp <d...@sqlite.org> wrote:
> On 4/1/17, Olivier Mascia <o...@integral.be> wrote: > > > So if someone can confirm/infirm this assertion (about length(DBYTES) not > > involving needless I/O), I'd love to read you. > > Confirmed. Content is not read from disk for the length() or typeof() > functions. https://www.sqlite.org/src/artifact/f1acf5744ce?ln=2675-2680 2432 /* Opcode: Column P1 P2 P3 P4 P5 2433 ** Synopsis: r[P3]=PX 2434 ** 2435 ** Interpret the data that cursor P1 points to as a structure built using 2436 ** the MakeRecord instruction. (See the MakeRecord opcode for additional 2437 ** information about the format of the data.) Extract the P2-th column 2438 ** from this record. If there are less that (P2+1) 2439 ** values in the record, extract a NULL. 2440 ** 2441 ** The value extracted is stored in register P3. 2442 ** 2443 ** If the column contains fewer than P2 fields, then extract a NULL. Or, [DD] Don't you mean "record" (or "row") instead of "column" above ? [DD] Isn't line 2441 a duplicate of lines 2438-2439 ? [DD] If neither is true above, that implies a column contains several fields, [DD] which would seem "denormalized"; Doesn't mean it's not valid, just that [DD] I can't quite groke it as written. 2444 ** if the P4 argument is a P4_MEM use the value of the P4 argument as 2445 ** the result. 2446 ** 2447 ** If the OPFLAG_CLEARCACHE bit is set on P5 and P1 is a pseudo-table cursor, 2448 ** then the cache of the cursor is reset prior to extracting the column. 2449 ** The first OP_Column against a pseudo-table after the value of the content 2450 ** register has changed should have this bit set. 2451 ** 2452 ** If the OPFLAG_LENGTHARG and OPFLAG_TYPEOFARG bits are set on P5 when [DD] on P5 *then* the result is ..., no? 2453 ** the result is guaranteed to only be used as the argument of a length() 2454 ** or typeof() function, respectively. The loading of large blobs can be 2455 ** skipped for length() and all content loading can be skipped for typeof(). 2456 */ 2457 case OP_Column: { _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
