add_unique_constraint = async (table_name, field_names) => {
  // TBD check that there are no problems with lenght of constraint name
  const sql = `alter table "${getTenantSchema()}"."${sqlsanitize(
    table_name
  )}" add CONSTRAINT "${sqlsanitize(table_name)}_${field_names
    .map((f) => sqlsanitize(f))
    .join("_")}_unique" UNIQUE (${field_names
    .map((f) => `"${sqlsanitize(f)}"`)
    .join(",")});`;
  sql_log(sql);
  await getMyClient().query(sql);
}
Add unique constraint
@param {string} table_name - table name
@param {string[]} field_names - list of columns (members of constraint)
@returns {Promise<void>} no result