From: drh Date: Thu, 25 Aug 2016 17:40:32 +0000 (+0000) Subject: Further refinement of the in-operator.md documentation. X-Git-Tag: version-3.15.0~110^2~38 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1373c3a8c52ea8f2ba2877f223476cbe61c729b7;p=thirdparty%2Fsqlite.git Further refinement of the in-operator.md documentation. FossilOrigin-Name: df0648373a50006ca18d692e12552d1d53d549e3 --- diff --git a/manifest b/manifest index cd1f8ff071..9f1b129892 100644 --- a/manifest +++ b/manifest @@ -1,5 +1,5 @@ -C Improvements\sto\sIN\soperator\scode\sgenerator\scomments.\s\sAvoid\sunnecessary\nCopy\soperations\son\sthe\sLHS\sof\sthe\sIN\soperator. -D 2016-08-25T15:46:25.026 +C Further\srefinement\sof\sthe\sin-operator.md\sdocumentation. +D 2016-08-25T17:40:32.626 F Makefile.in cfd8fb987cd7a6af046daa87daa146d5aad0e088 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434 F Makefile.msc d66d0395c38571aab3804f8db0fa20707ae4609a @@ -346,7 +346,7 @@ F src/global.c c45ea22aff29334f6a9ec549235ac3357c970015 F src/hash.c 55b5fb474100cee0b901edaf203e26c970940f36 F src/hash.h ab34c5c54a9e9de2e790b24349ba5aab3dbb4fd4 F src/hwtime.h 747c1bbe9df21a92e9c50f3bbec1de841dc5e5da -F src/in-operator.md 973fe4522b871fb8cf683d8453760f4f19ac68c8 +F src/in-operator.md 9627b332c40228c0cb756eff1d84471b397539be F src/insert.c a255eb795cf475e7a0659297144fc80f70eb4e30 F src/legacy.c 75d3023be8f0d2b99d60f905090341a03358c58e F src/loadext.c dd7a2b77902cc66c22555aef02e1a682554b7aec @@ -1521,7 +1521,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0 -P 25033ee94538289ba7e0147da30a18300047123f -R e1cedb5c8edd4d27c5fcda8527491fbe +P b6344298783a1207cba3f635939ddc9ba922ab67 +R 0bc7dc0041a27b5ec53385d0f7163e25 U drh -Z c3029179ef3a13ce81541f0730bc01a8 +Z 0df057355417cbdb73d372028cbbe733 diff --git a/manifest.uuid b/manifest.uuid index f23c36e283..fa403130a1 100644 --- a/manifest.uuid +++ b/manifest.uuid @@ -1 +1 @@ -b6344298783a1207cba3f635939ddc9ba922ab67 \ No newline at end of file +df0648373a50006ca18d692e12552d1d53d549e3 \ No newline at end of file diff --git a/src/in-operator.md b/src/in-operator.md index 0c9480234d..ecd0b97e3a 100644 --- a/src/in-operator.md +++ b/src/in-operator.md @@ -61,9 +61,7 @@ algorithm is suboptimal, especially if there are many rows on the RHS. The following procedure computes the same answer as the simple full-scan algorithm, though it does so with less work in the common case. This -is the algorithm that is implemented in SQLite. The steps must occur -in the order specified. Steps 1 and 3 are optional. All other steps -are required for correctness. +is the algorithm that is implemented in SQLite. 1. If the RHS is a constant list of length 1 or 2, then rewrite the IN operator as a simple expression. Implement @@ -78,25 +76,21 @@ are required for correctness. IN operator is used for membership testing. If the IN operator is driving a loop, then skip this step entirely. - 2. If the RHS is empty, return FALSE. + 2. Check the LHS to see if it is a partial-NULL and if it is, jump + ahead to step 4. - 3. If the LHS is a total-NULL, then return NULL. + 3. Do a binary search for the RHS using the LHS as a probe. If + an exact match is found, return TRUE. - 4. If the LHS is non-NULL, then use the LHS as a probe in a binary - search of the RHS + 4. If we do not need to distingish between FALSE and NULL, + then return FALSE. - 4-A. If the binary search finds an exact match, return TRUE - - 4-B. If the RHS is known to be not-null, return FALSE - - 5. At this point, it is known that the result cannot be TRUE. All - that remains is to distinguish between NULL and FALSE. - If a NOT-TRUE result is acceptable, then return NOT-TRUE now. + 5. If the RHS is non-NULL then return FALSE. 6. For each row in the RHS, compare that row against the LHS and - if the result is NULL, immediately return NULL. This step is - essentially the "Simple Full-scan Algorithm" above with the - tests for TRUE removed, since we know that the result cannot be - TRUE at this point. + if the result is NULL, immediately return NULL. In the case + of a scalar IN operator, we only need to look at the very first + row the RHS because for a scalar RHS, all NULLs will always come + first. If the RHS is empty, this step is a no-op. 7. Return FALSE.