Conditions in prepared statements in postgres - postgresql

Question

I need to add a condition inside prepared statement in postgres.
Pseudocode (doesn't works, fires an error "argument of WHERE must be type boolean, not type text"):
if (nameFilter) {
whereParam = `name LIKE %${nameFilter}%`
} else {
whereParam = "true"
}
let query = prepare("SELECT * FROM users WHERE $1", whereParam);
Pseudocode (works but looks ugly):
if (nameFilter) {
likeParam = `%${nameFilter}%`
} else {
likeParam = "%"
}
let query = prepare("SELECT * FROM users WHERE name LIKE $1", likeParam);
For some reasons(query is really complex with a bunch of AND) manipulations with a string is not an option, so this will not help
if (nameFilter) {
q = `SELECT * FROM users WHERE name LIKE $1`
} else {
q = "SELECT * FROM users"
}
let query = prepare(q, nameFilter);
Desirable to have statement similar to SELECT * FROM users WHERE $1 AND $2 AND $3 ...
Any suggestions?

Answer 1

This query will work for you.
select * from users where
case
when coalesce($1, '') = '' then true
else (name ~ $1)
end;

Answer 2

The only thing you can pass as a parameter is a constant; you cannot pass part of an SQL query like name LIKE '%pattern%'.
So if your query is really different every time, you have to construct the SQL string in your code, just like you say you cannot do "for some reasons".
It may be annoying, but there is no other way.
When you construct an SQL statement, make sure you never concatenate strings like this:
sql = "SELECT * FROM users WHERE username ='" + username + "'"
because that would be vulnerable to SQL injection.