{"id":138,"date":"2016-03-20T00:09:11","date_gmt":"2016-03-20T00:09:11","guid":{"rendered":"http:\/\/hammod.com\/?p=138"},"modified":"2021-10-03T17:31:03","modified_gmt":"2021-10-03T17:31:03","slug":"three-value-logic","status":"publish","type":"post","link":"http:\/\/hammod.com\/?p=138","title":{"rendered":"Three value logic"},"content":{"rendered":"

\"three_value_logic\"<\/a>In SQL, When a NULL is involved in a comparison operation, the result is considered to be UNKNOWN (it may be TRUE or it may be FALSE). Hence, SQL uses a three valued logic with values TRUE, FALSE, and UNKNOWN instead of the standard two-valued (Boolean) logic with values TRUE or FALSE. It is therefore necessary to define the results (or truth values) of three-valued logical expressions when the logical connectives AND, OR, and NOT are used.<\/p>\n

[table caption=”Three-Valued logic with AND” width=”350″ colwidth=”100|50|50″ colalign=”left|left|left|left”]
\nAND<\/span>,TRUE,FALSE,UNKNOWN,
\nTURE<\/strong>, T, F, UNK
\nFALSE<\/strong>, F,F,F
\nUNKOWN<\/strong>,UNK,F,UNK
\n[\/table]<\/p>\n

[table caption=”Three-Valued logic with OR ” width=”350″ colwidth=”100|50|50″ colalign=”left|left|left|left”]
\nOR <\/span>,TRUE,FALSE,UNKNOWN,
\nTURE<\/strong>, T, T,T
\nFALSE<\/strong>, T,F,UNK
\nUNKOWN<\/strong>,T,UNK,UNK
\n[\/table]<\/p>\n

[table caption=”Three-Valued logic with NOT” width=”150″ colwidth=”100|50|50″ colalign=”left|left”]
\nNOT <\/span>,
\nTURE<\/strong>, F
\nFALSE<\/strong>, T
\nUNKOWN<\/strong>,UNK
\n[\/table]<\/p>\n

Reference:<\/p>\n

Elmasri, R., & Navathe, S. (2011). Fundamentals of database systems<\/i>. Boston: Addison-Wesley.<\/p>\n","protected":false},"excerpt":{"rendered":"

In SQL, When a NULL is involved in a comparison operation, the result is considered to be UNKNOWN (it may be TRUE or it may be FALSE). Hence, SQL uses a threeRead More…<\/a><\/p>\n","protected":false},"author":1,"featured_media":146,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/posts\/138"}],"collection":[{"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/hammod.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=138"}],"version-history":[{"count":28,"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/posts\/138\/revisions"}],"predecessor-version":[{"id":229,"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/posts\/138\/revisions\/229"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/hammod.com\/index.php?rest_route=\/wp\/v2\/media\/146"}],"wp:attachment":[{"href":"http:\/\/hammod.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=138"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/hammod.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=138"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/hammod.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=138"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}