creating comma seperated string to be given as input to sql “IN” clause

Question

I want a string to be given as input to the SQL \"IN\" clause,where in i want a list of strings separated by commas

Answer 1

This does the job:

public String separateByComma(List<String> input) {

   // check for valid input!!

   public StringBuilder sb = new StringBuilder(input.get(0));
   for (int i = 1; i < input.size(); i++)
     sb.append(",").append(input.get(i));

   return sb.toString();
}

BTW - you may need the Strings boxed in double quotes:

public String separateByCommaForSQL(List<String> input) {

   // check for valid input!!

   public StringBuilder sb = new StringBuilder("\""+input.get(0)+ "\"");
   for (int i = 1; i < input.size(); i++)
     sb.append(",\"").append(input.get(i)).append("\"");

   return sb.toString();
}

Answer 2

An unusual solution: If the Strings are in ArrayList or LinkedList (sub class of java.util.AbstractCollection), call toString() which returns "[e1, e2, e3...]". Then you could handle the string.

Answer 3

As pointed out by the other answers, there are many helpers you can use to do the joining.

I'd like to add a caveat:

Be aware that most DBMS have a upper limit on the number of values that you can concatenate like this. We have run into this before; if you are not certain that you will never have more than a few dozen values or so, you must make sure you do not exceed this limit (which is different for every DBMS, sometimes even configurable).

The limit usually comes either from a limit on the total size of an SQL statement, or an explicit limit on the number of values in a comma-separated list.

If you run into this problem, an alternative is to create a temporary (or permanent) table for the values list, and INSERT your values into this table. Then you can use a WHERE xxx IN (SELECT column FROM helpertable) instead of putting the list into the SQL statement. This avoids the maximum length problem; it is also probably faster if you need to re-use the list. It' more hassle (and probably slower) if you only need the list once though...

Answer 4

You should use a PreparedStatement so your strings are escaped automatically if necessary and you will be protected from sql injection.

First, generate a statement with a marker for each element in the list. For example:

select id, name from users where name in (?, ?, ?)

Then loop over your list and set the values in the statement.

Take a look at this question for details:

What is the best approach using JDBC for parameterizing an IN clause?

Answer 5

You can use guava's Joiner:

Joiner.on(",").join(inputsList);

Answer 6

You may use org.apache.commons.lang.StringUtils.join() method, or implement join operation yourself.