MySQL逗号连接字符串在Java中用逗号

Question

I am trying to concatenate two ID numbers together but add a comma between them to separate from each other. I know the mysql statement to use but I am having difficulty translating this to a string in my java program. I can get it to work without the comma but I can't seem to figure out the syntax for adding the comma.

Here is my attempt:

query = "UPDATE table SET idColumn = concat(idColumn, ','"+idNum+") WHERE word = '"+wordVariable+"' ";

To clarify, I have a word table which contains a word column and an ID number column. As an example, my ID column might contain a single number as the ID but after multiple concatenations it might look like:

2,5,4,7,1

Answer 1

Change your query to:

query = "UPDATE table SET idColumn = concat(idColumn, ',"+idNum+"') WHERE word = '"+wordVariable+"' ";

I Think you have made mistake on using inverted commas.

Or you can add comma after ','.

query = "UPDATE table SET idColumn = concat(idColumn, ',' , '"+idNum+"') WHERE word = '"+wordVariable+"' ";

Answer 2

Change :

query = "UPDATE table 
         SET idColumn = concat(idColumn, ','"+idNum+") 
         WHERE word = '"+wordVariable+"' ";

To :

query = "UPDATE table SET idColumn = concat( idColumn, ',', ? ) WHERE word = ? ";

You were missing a , comma after ',' in the concat .

And using an instance of PreparedStatement you can set values for query placeholders.

pst.setInt( 1, idNum );
pst.setString( 2, wordVariable );

And, I think, your data table design is not correct on idColumn . Instead of storing comma separated values, you better use a normalized form of tables and data.