转换CLOB字段类型为VARCHAR2
不支持的语句不支持的用法例子SELECT DISTINCT

SELECT DISTINCT clobCol from...

SELECT clause

ORDER BY

SELECT... ORDER BY clobCol

SELECT clause

GROUP BY

SELECT avg(num) FROM...

GROUP BY clobCol

UNION, INTERSECT, MINUS

(Note that UNION ALL works for LOBs.)

SELECT clobCol1 from tab1 UNION SELECT clobCol2 from tab2;

Join queries

SELECT... FROM... WHERE tab1.clobCol = tab2.clobCol

Index columns

CREATE INDEX clobIndx ON tab(clobCol)...