java - Difference between RETURN_GENERATED_KEYS and specifying the generated column names -


what difference between preparestatement(string sql, int autogeneratedkeys) , preparestatement(string sql, string[] columnnames) methods of jdbc connection class?

the javadoc both indicates returned preparedstatement object capable of returning auto-generated keys if sql statement insert statement. in case of first api, statement.return_generated_keys needs passed autogeneratedkeys parameter. in case of second api, names of generated columns passed string array.

what reasons using 1 on other?

i noticed spring's simplejdbcinsert class prefers variant column names specified: abstractjdbcinsert.preparestatementforgeneratedkeys

why that?

the reasons convenience, flexibility, performance , compatibility. example, database cannot know columns auto-generated or not, default drivers return all columns when using statement.return_generated_keys.

this can have impact on performance because:

  1. all values need transferred database client,
  2. on databases requires query on metadata know columns fetch.

for example, driver postgresql append returning * (so has point 1 worry about), while firebird driver (which maintain) has query metadata.

some database drivers default return column not directly useful (eg oracle - used to? - return rowid, means have query actual field yourself), , databases return primary key, while there might other generated fields, , believe database drivers return last generated key, if table doesn't use identity field(!).

the methods preparestatement(string sql, string[] columnnames) , preparestatement(string sql, int[] columnindexes) give more control (if supported), returned. if know fields need or want, can specify them , fields, without having worry differences in behavior return_generated_keys.

depending on implementation, 1 taking string[] columnnames efficient names can put in verbatim, while int[] columnindexes might still require metadata query actual names.


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