sql - the use of quote_ident() in a plpgsql function -

i new in creating plpgsql function.i need clarifications regarding use of quote_ident() (and quote_literal()) on dynamic commands being executed inside function. hope give me specific explanation on how worked inside function. tia

here's example of it:

execute 'update tbl set ' || quote_ident(colname) || ' = ' || quote_literal(newvalue) || ' key = ' || quote_literal(keyvalue); 

quote_ident used identifiers quoting. quote_literal used string quoting.

postgres=# select quote_ident('tablename'); ┌─────────────┐ │ quote_ident │ ╞═════════════╡ │ tablename   │ └─────────────┘ (1 row)  postgres=# select quote_ident('special name'); ┌────────────────┐ │  quote_ident   │ ╞════════════════╡ │ "special name" │ └────────────────┘ (1 row)  postgres=# select quote_literal(e'some text special char"\'"'); ┌───────────────────────────────────┐ │           quote_literal           │ ╞═══════════════════════════════════╡ │ 'some text special char"''"' │ └───────────────────────────────────┘ (1 row) 

what identifier? names of tables, columns, schemas, sequences, ... literal? - text value (but can value of type). both function search , replace special chars, different rules - identifiers , strings different in sql.

now - these functions little bit obsolete. quote_literal should replaced clause using (better performance), quote_ident should replaced formatting function format (due better readability):

execute format('update tbl set %i=$1 key=$2', colname)    using newvalue, keyvalue; 

or format function

execute format('update tbls set %i=%l key=%l', colname, newvalue, keyvalue); 

without quoting dynamic sql a) should not work (fails on syntax error), b) be unsafe against sql injection.