Question

I have string like

order by o desc,b asc

Here I want to replace o and b columns of this clause by table_o and table_b and output

order by table_o desc, table_b asc

I am using replace function for that but output becomes like

table_order table_by table_o desc,table_b asc

How to solve this problem using regular expression?

One more example

"order by orders desc, bye asc"

should be replaced as

"order by table_orders desc, table_bye asc"

Answer 1

Here is one possible solution. [You might have to tweak spaces around desc asc and , based on your actual SQL]

    String str = "select a,b,c * from Table order by o desc,b asc,c,d";
    System.out.println(str.replaceAll(
            "(.*order by )?(\\w+)( desc| asc)?(,|$)", "$1table_$2$3$4"));

Result

select a,b,c * from Table order by table_o desc,table_b asc,table_c,table_d

Visual Regex

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Regex details

• (.*order by)? => will match select a,b,c * from Table order by =>back ref $1
• (\\w+)               => will match column name =>back ref $2
• ( desc| asc)? => will match desc or asc => back ref $3
• (,|$)                 => will match trailing comma or endof line => back ref $4

Please Note : this solution only works with simple sql queries, and would produce wrong result if the order byclause is part of inner query of a complex SQL. Moreover Regex is not can not ideal tool to parse SQL syntax

See this link Regular expression to match common SQL syntax?

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   If full-fledged SQL parsing is required, Its better to use either SQL parsers or Parser generators like ANTLR to parse SQL. See this link for list of available ANTLR SQL grammer