怎样分别求函数的左极限和右极限

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select * from tbl_Articles WHERE ArticleID=2623879 LIMIT 0,1
select * from tbl_Articles_data WHERE ArticleID=2623879 LIMIT 0,1
select * from tbl_Articles_sphinx where id=2623879 LIMIT 0,1
SELECT ArticleID,Title FROM tbl_Articles WHERE ArticleID IN(1096719,1076199,1116615,1086582,1093865,1064449,1103556,1070092,1069505,1117043,1099791,1104434,1044735,1101527,1101273,1090537,1096793,1080432,1044745,1065773,1104955,1107965,1104941,1126964,1109308,1122653,1091621,1010909,1044442,1089454) ORDER BY field (ArticleID,1096719,1076199,1116615,1086582,1093865,1064449,1103556,1070092,1069505,1117043,1099791,1104434,1044735,1101527,1101273,1090537,1096793,1080432,1044745,1065773,1104955,1107965,1104941,1126964,1109308,1122653,1091621,1010909,1044442,1089454)