Hologres use PostgreSQL 11 semantics but only support a subset of all the functions supported by PostgreSQL. Below tables list all functions Hologres supported currently. For detailed information please refer to PostgreSQL document.

Mathematcial Functions

Function Supported Added by Hologres
abs(bigint) Yes No
abs(int) Yes No
abs(float8) Yes No
abs(float4) Yes No
abs(numeric) Yes No
cbrt(dp) Yes No
ceil(dp ) Yes No
ceil(numeric) Yes No
ceiling(dp ) Yes No
ceiling(numeric) Yes No
degrees(dp) Yes No
exp(dp) Yes No
exp(numeric) Yes No
floor(dp ) Yes No
floor(numeric) Yes No
ln(dp) Yes No
ln(numeric) Yes No
log(dp) Yes No
log(numeric) Yes No
log(b numeric, x numeric) Yes No
mod(bigint, x) Yes No
mod(int, x) Yes No
pi() Yes No
power(a dp, b dp) Yes No
power(a numeric, b numeric) Yes No
radians(dp) Yes No
round(dp ) Yes No
round(numeric) Yes No
round(v numeric, s int) Yes No
sign(dp ) Yes No
sign(numeric) Yes No
sqrt(dp) Yes No
sqrt(numeric) Yes No
trunc(dp) Yes No
trunc(numeric) Yes No
trunc(v numeric, s int) Yes No
width_bucket(operand numeric, b1 numeric, ...) Yes No
random() Yes No

Trigonometric Functions

Function Supported Added by Hologress
acos(bigint) Yes No
acos(int) Yes No
acos(float8) Yes No
acos(float4) Yes No
acos(numeric) Yes No
asin(bigint) Yes No
asin(int) Yes No
asin(float8) Yes No
asin(float4) Yes No
asin(numeric) Yes No
atan(bigint) Yes No
atan(int) Yes No
atan(float8) Yes No
atan(float4) Yes No
atan(numeric) Yes No
atan2(bigint) Yes No
atan2(int) Yes No
atan2(float8) Yes No
atan2(float4) Yes No
atan2(numeric) Yes No
cos(bigint) Yes No
cos(int) Yes No
cos(float8) Yes No
cos(float4) Yes No
cos(numeric) Yes No
cot(bigint) Yes No
cot(int) Yes No
cot(float8) Yes No
cot(float4) Yes No
cot(numeric) Yes No
sin(bigint) Yes No
sin(int) Yes No
sin(float8) Yes No
sin(float4) Yes No
sin(numeric) Yes No
tan(bigint) Yes No
tan(int) Yes No
tan(float8) Yes No
tan(float4) Yes No
tan(numeric) Yes No

String Functions and Operators

Function Supported Added by Hologress
string string
bit_length(string) Yes No
char_length(string) Yes No
lower(string) Yes No
octet_length(string) Yes No
position(substring in string) Yes No
substring(string [from int] [for int]) Yes No
substring(string from pattern) Yes No
substring(string from pattern for escape) Yes No
trim([leading trailing both] [characters] from string)
trim([lea tra both] [from] string [, char] )
upper(string) Yes No

Other Postgres String Functions

Function Supported Added by Hologress
ascii(string) Yes No
btrim(string text [, characters text]) Yes No
chr(int) Yes No
concat(str "any" [, str "any" [, ...] ]) Yes No
initcap(string) Yes No
length(string) Yes No
lpad(string text, length int [, fill text]) Yes No
ltrim(string text [, characters text]) Yes No
md5(string) Yes No
parse_ident(quali_iden text [,...] ) Yes No
quote_ident(string text) Yes No
quote_literal(string text) Yes No
regexp_matches(string text, pattern text ) Yes No
regexp_replace(str text, pat text, replace text ) Yes No
regexp_split_to_array(string text, pattern text ) Yes No
regexp_split_to_table(string text, pattern text ) Yes No
repeat(string text, number int) Yes No
replace(string text, from text, to text) Yes No
rpad(string text, length int [, fill text]) Yes No
rtrim(string text [, characters text]) Yes No
strpos(string, substring) Yes No
substr(string, from [, count]) Yes No
starts_with(string, prefix) Yes No
to_hex(number int or bigint) Yes No
translate(string text, from text, to text) Yes No

Pattern Matching

Function Supported Added by Hologress
like Yes No
not like Yes No
similar to Yes No
not similar to Yes No
rlike ~ Yes No
rlike !~* Yes No
rlike ~* Yes No
rlike !~ Yes No
substring() Yes No
regexp_replace() Yes No
regexp_split_to_table Yes No
regexp_split_to_array Yes No

Date/Time Formating Functions

Function Supported Added by Hologress
to_char(timestamp, text) Yes No
to_char(int, text) Yes No
to_char(double precision, text) Yes No
to_date(text, text) Yes No
to_number(text, text) Yes No
to_timestamp(text, text) Yes No
date - date Yes No
clock_timestamp() Yes No
current_date Yes No
current_timestamp Yes No
date_part(text, timestamp) Yes No
date_trunc(text, timestamp) Yes No
extract(field from timestamp) Yes No
isfinite(date) Yes No
isfinite(timestamp) Yes No
isfinite(interval) Yes No
make_date(year int, month int, day int) Yes No
localtimestamp Yes No
now() Yes No
statement_timestamp() Yes No
timeofday() Yes No
transaction_timestamp() Yes No
to_timestamp(double precision) Yes No

Conditional Expressions

Function Supported Added by Hologress
case Yes No
coalesce Yes No
nullif Yes No
greatest Yes No
least Yes No

Array Functions

Function Supported Added by Hologress
array_append(anyarray, anyelement) Yes No
array_dims(anyarray) Yes No
array_lower(anyarray, int) Yes No
array_prepend(anyelement, anyarray) Yes No
array_upper(anyarray, int) Yes No
unnest(anyarray) Yes No

General-Purpose Aggregate Functions

Function Supported Added by Hologress
array_agg(bigint) Yes No
array_agg(bool) Yes No
array_agg(text) Yes No
array_agg(float8) Yes No
array_agg(float4) Yes No
array_agg(int) Yes No
avg(bigint) Yes No
avg(float8) Yes No
avg(float4) Yes No
avg(int) Yes No
bit_and(bigint) Yes No
bit_and(int) Yes No
bit_or(bigint) Yes No
bit_or(int) Yes No
bool_and(bool) Yes No
bool_or(bool) Yes No
cout(*) Yes No
cout(bigint) Yes No
cout(numeric) Yes No
every(bool) Yes No
max(bigint) Yes No
max(float8) Yes No
max(float4) Yes No
max(int) Yes No
max(numeric) Yes No
min(bigint) Yes No
min(float8) Yes No
min(float4) Yes No
min(int) Yes No
min(numeric) Yes No
sum(bigint) Yes No
sum(float8) Yes No
sum(float4) Yes No
sum(int) Yes No
sum(numeric) Yes No
string_agg(expression, delimiter) Yes No
corr(Y, X) Yes No
covar_pop(Y, X) Yes No
covar_samp(Y, X) Yes No
regr_avgx(Y, X) Yes No
regr_avgy(Y, X) Yes No
regr_count(Y, X) Yes No
regr_intercept(Y, X) Yes No
regr_r2(Y, X) Yes No
regr_slope(Y, X) Yes No
regr_sxx(Y, X) Yes No
regr_sxy(Y, X) Yes No
regr_syy(Y, X) Yes No
stddev(int) Yes No
stddev(numeric) Yes No
stddev(float8) Yes No
stddev_pop(int) Yes No
stddev_pop(numeric) Yes No
stddev_pop(float8) Yes No
stddev_samp(int) Yes No
stddev_samp(numeric) Yes No
stddev_samp(float8) Yes No
variance(int) Yes No
variance(numeric) Yes No
var_pop(float8) Yes No
var_pop(int) Yes No
var_pop(numeric) Yes No
var_samp(float8) Yes No
var_samp(int) Yes No
var_samp(numeric) Yes No

Ordered-Set Aggregate Functions

Function Supported Added by Hologress
GROUPING(args...) Yes Yes

Window Functions

Function Supported Added by Hologress
row_number() Yes No
rank() Yes No
dense_rank() Yes No
percent_rank() Yes No
lag() Yes No
lead() Yes No
first_value() Yes No
last_value() Yes No

Subquery Expressions

Function Supported Added by Hologress
EXISTS (subquery) Yes No
IN (subquery) Yes No
NOT IN (subquery) Yes No
ANY (subquery) Yes No
SOME (subquery) Yes No

Row and Array Comparisons

Function Supported Added by Hologress
NOT IN (values,...) Yes No
IN (values,...) Yes No

Set Returning functions

Function Supported Added by Hologress
generate_series(start, stop) Yes No
generate_series(start, stop, step) Yes No
generate_series(start, stop, step interval) Yes No
generate_subscripts(array anyarray, dim int) Yes No

Session Information Functions

Function Supported Added by Hologress
current_catalog Yes No
current_database() Yes No
current_query() Yes No
current_role Yes No
current_schema[()] Yes No
current_schemas(boolean) Yes No
current_user Yes No
inet_client_addr() Yes No
inet_client_port() Yes No
inet_server_addr() Yes No
inet_server_port() Yes No
pg_backend_pid() Yes No
pg_blocking_pids(int) Yes No
session_user Yes No
user Yes No
version() Yes No
current_setting(setting_name) Yes No

Access Privilege Inquiry Functions

Function Supported Added by Hologress
has_any_column_privilege(user, table, privilege) Yes No
has_any_column_privilege(table, privilege) Yes No
has_column_privilege(user, table, column, privilege) Yes No
has_column_privilege(table, column, privilege) Yes No
has_database_privilege(user, database, privilege) Yes No
has_database_privilege(database, privilege) Yes No
has_foreign_data_wrapper_privilege(user, fdw, privilege) Yes No
has_foreign_data_wrapper_privilege(fdw, privilege) Yes No
has_function_privilege(user, function, privilege) Yes No
has_function_privilege(function, privilege) Yes No
has_language_privilege(user, language, privilege) Yes No
has_language_privilege(language, privilege) Yes No
has_schema_privilege(user, schema, privilege) Yes No
has_schema_privilege(schema, privilege) Yes No
has_server_privilege(user, server, privilege) Yes No
has_server_privilege(server, privilege) Yes No
has_table_privilege(user, table, privilege) Yes No
has_table_privilege(table, privilege) Yes No
has_tablespace_privilege(user, tablespace, privilege) Yes No
has_tablespace_privilege(tablespace, privilege) Yes No
has_type_privilege(user, type, privilege) Yes No
has_type_privilege(type, privilege) Yes No
pg_has_role(user, role, privilege) Yes No
pg_has_role(role, privilege) Yes No

Public API Functions

Standard PostgreSQL functions cannot meet all business requirements, so Hologres added some new functions as public API which can be used to simplify development process. Next chapter will describe public API functions in detail.