Redrock Postgres Documentation
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JDBC escapes

The JDBC specification (like the ODBC specification) acknowledges the fact that some vendor specific SQL may be required for certain RDBMS features. To aid developers in writing portable JDBC applications across multiple database products, a special escape syntax is used to specify the generic commands the developer wants to be run. The JDBC driver translates these escape sequences into native syntax for its specific database. For more information consult the Java DB Technical Documentation.

The parsing of the sql statements for these escapes can be disabled using Statement.setEscapeProcessing(false) .

Connection.nativeSQL(String sql) provides another way to have escapes processed. It translates the given SQL to SQL suitable for the PostgreSQL backend.

Example 8.1. Using JDBC escapes

To use the JDBC escapes, you simply write your SQL replacing date/time literal values, outer join and functions by the JDBC escape syntax. For example:

ResultSet rs = st.executeQuery("SELECT {fn week({d '2005-01-24'})}");

is the portable version for

ResultSet rs = st.executeQuery("SELECT extract(week from DATE '2005-01-24')");

Escape for like escape character

You can specify which escape character to use in strings comparison (with LIKE ) to protect wildcards characters (’%’ and ‘_’) by adding the following escape : {escape 'escape-character'} . The driver supports this only at the end of the comparison expression.

For example, you can compare string values using ‘|’ as escape character to protect ‘_’ :

rs = stmt.executeQuery("select str2 from comparisontest where str1 like '|_abcd' {escape '|'} ");

Escape for outer joins

You can specify outer joins using the following syntax: {oj table (LEFT|RIGHT|FULL) OUTER JOIN (table | outer-join) ON search-condition}

For example :

ResultSet rs = stmt.executeQuery("select * from {oj a left outer join b on (a.i=b.i)} ");

Date-time escapes

The JDBC specification defines escapes for specifying date, time and timestamp values which are supported by the driver.

  • date : {d 'yyyy-mm-dd'} which is translated to DATE 'yyyy-mm-dd'
  • time : {t 'hh:mm:ss'} which is translated to TIME 'hh:mm:ss'
  • timestamp : {ts 'yyyy-mm-dd hh:mm:ss.f...'} which is translated to TIMESTAMP 'yyyy-mm-dd hh:mm:ss.f' The fractional seconds (.f…) portion of the TIMESTAMP can be omitted.

Escaped scalar functions

The JDBC specification defines functions with an escape call syntax : {fn function_name(arguments)} . The following tables show which functions are supported by the PostgreSQL driver. The driver supports the nesting and the mixing of escaped functions and escaped values. The appendix C of the JDBC specification describes the functions.

Some functions in the following tables are translated but reported as not supported because they are duplicating or changing their order of the arguments. While this is harmless for literal values or columns, it will cause problems when using prepared statements. For example " {fn right(?,?)} " will be translated to " substring(? from (length(?)+1-?)) “. As you can see the translated SQL requires more parameters than before the translation but the driver will not automatically handle this.

Table 8.1. Supported escaped numeric functions

function reported as supported translation comments
abs(arg1) yes abs(arg1)
acos(arg1) yes acos(arg1)
asin(arg1) yes asin(arg1)
atan(arg1) yes atan(arg1)
atan2(arg1, arg2) yes atan2(arg1, arg2)
ceiling(arg1) yes ceil(arg1)
cos(arg1) yes cos(arg1)
cot(arg1) yes cot(arg1)
degrees(arg1) yes degrees(arg1)
exp(arg1) yes exp(arg1)
floor(arg1) yes floor(arg1)
log(arg1) yes ln(arg1)
log10(arg1) yes log(arg1)
mod(arg1, arg2) yes mod(arg1, arg2)
pi(arg1) yes pi(arg1)
power(arg1, arg2) yes pow(arg1, arg2)
radians(arg1) yes radians(arg1)
rand() yes random()
rand(arg1) yes setseed(arg1)*0+random() The seed is initialized with the given argument and a new random value is returned.
round(arg1, arg2) yes round(arg1, arg2)
sign(arg1) yes sign(arg1)
sin(arg1) yes sin(arg1)
sqrt(arg1) yes sqrt(arg1)
tan(arg1) yes tan(arg1)
truncate(arg1, arg2) yes trunc(arg1, arg2)

Table 8.2. Supported escaped string functions

function reported as supported translation comments
ascii(arg1) yes ascii(arg1)
char(arg1) yes chr(arg1)
concat(arg1, arg2…) yes (arg1
insert(arg1, arg2, arg3, arg4) no overlay(arg1 placing arg4 from arg2 for arg3) This function is not supported since it changes the order of the arguments which can be a problem (for prepared statements by example).
lcase(arg1) yes lower(arg1)
left(arg1, arg2) yes substring(arg1 for arg2)
length(arg1) yes length(trim(trailing from arg1))
locate(arg1, arg2) no position(arg1 in arg2)
locate(arg1, arg2, arg3) no (arg2*sign(position(arg1 in substring(arg2 from arg3)+position(arg1 in substring(arg2 from arg3)) Not supported since the three arguments version duplicate and change the order of the arguments.
ltrim(arg1) yes trim(leading from arg1)
repeat(arg1, arg2) yes repeat(arg1, arg2)
replace(arg1, arg2, arg3) yes replace(arg1, arg2, arg3) Only reported as supported by 7.3 and above servers.
right(arg1, arg2) no substring(arg1 from (length(arg1)+1-arg2)) Not supported since arg2 is duplicated.
rtrim(arg1) yes trim(trailing from arg1)
space(arg1) yes repeat(’ ‘, arg1)
substring(arg1, arg2) yes substr(arg1, arg2)
substring(arg1, arg2, arg3) yes substr(arg1, arg2, arg3)
ucase(arg1) yes upper(arg1)
soundex(arg1) no soundex(arg1) Not supported since it requires the fuzzystrmatch contrib module.
difference(arg1, arg2) no difference(arg1, arg2) Not supported since it requires the fuzzystrmatch contrib module.

Table 8.3. Supported escaped date/time functions

function reported as supported translation comments
curdate() yes current_date
curtime() yes current_time
dayname(arg1) yes to_char(arg1, ‘Day’)
dayofmonth(arg1) yes extract(day from arg1)
dayofweek(arg1) yes extract(dow from arg1)+1 We must add 1 to be in the expected 1-7 range.
dayofyear(arg1) yes extract(doy from arg1)
hour(arg1) yes extract(hour from arg1)
minute(arg1) yes extract(minute from arg1)
month(arg1) yes extract(month from arg1)
monthname(arg1) yes to_char(arg1, ‘Month’)
now() yes now()
quarter(arg1) yes extract(quarter from arg1)
second(arg1) yes extract(second from arg1)
week(arg1) yes extract(week from arg1)
year(arg1) yes extract(year from arg1)
timestampadd(argIntervalType, argCount, argTimeStamp) yes ((interval according to argIntervalType and argCount)+argTimeStamp) an argIntervalType value of SQL_TSI_FRAC_SECOND is not implemented since backend does not support it
timestampdiff(argIntervalType, argTimeStamp1, argTimeStamp2) not extract((interval according to argIntervalType) from argTimeStamp2-argTimeStamp1 ) only an argIntervalType value of SQL_TSI_FRAC_SECOND, SQL_TSI_FRAC_MINUTE, SQL_TSI_FRAC_HOUR or SQL_TSI_FRAC_DAY is supported

Table 8.4. Supported escaped misc functions

function reported as supported translation comments
database() yes current_database() Only reported as supported by 7.3 and above servers.
ifnull(arg1, arg2) yes coalesce(arg1, arg2)
user() yes user