When doing an UPDATE or DELETE using a multi-column index where only a few

of the earlier columns of the index are useful for the index lookup,
postpone doing the main table seek until after all WHERE clause constraints
have been evaluated, in case those constraints can be covered by unused
later terms of the index, thus avoiding unnecessary main table seeks.

FossilOrigin-Name: 7fee0b1075d622835dc6828c061be516102da9e2809f52d9ab7c4bbef7dfb871

diff --cc manifest
index bdf8aea8695de826dcd03426b754aef2c192bea8,b1f787fcdf1d37db86e4ca1568071ce3de73fba7..9ccd5651378f2d1e84db395b267ba810f983da57
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Update\sthe\sversion\snumber\sto\s3.34.0\sfor\sthe\snext\sdevelopment\scycle.
- D 2020-08-14T21:37:32.306
 -C Optimizations\sto\sthe\slogic\sthat\sconverts\smain\stable\saccesses\sinto\sequivalent\nindex\saccesses.\s\sCode\sis\snow\sslightly\ssmaller\sand\sfaster\sthan\strunk.
 -D 2020-08-14T21:32:16.882
++C When\sdoing\san\sUPDATE\sor\sDELETE\susing\sa\smulti-column\sindex\swhere\sonly\sa\sfew\nof\sthe\searlier\scolumns\sof\sthe\sindex\sare\suseful\sfor\sthe\sindex\slookup,\npostpone\sdoing\sthe\smain\stable\sseek\suntil\safter\sall\sWHERE\sclause\sconstraints\nhave\sbeen\sevaluated,\sin\scase\sthose\sconstraints\scan\sbe\scovered\sby\sunused\nlater\sterms\sof\sthe\sindex,\sthus\savoiding\sunnecessary\smain\stable\sseeks.
++D 2020-08-14T21:51:02.627
  F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
  F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@@ -1879,7 -1879,7 +1879,8 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
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  U drh
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 -Z a854ac35ef1e1fa9d5bc731176f5cbf6
++Z 5d0dae315c2c275d1ce9160adcb43cdc

diff --cc manifest.uuid
index 3698b1361b993d928e067e1f7b73ab220e23b7bf,b2a145b0f4813f51d08cd56a3a50d2ee4a34b895..44b1baae1f1800482d4d0e1bc0f5b7d2c6bad7a6
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 70f34f3df5358d36c8578afbc05756450c46da36b8dce339ed87fc0b9d4057cb
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++7fee0b1075d622835dc6828c061be516102da9e2809f52d9ab7c4bbef7dfb871