Simple SQL Exercices

SQL, or “Structured Query Language”, is a means of asking questions of, and updating data in, relational databases. Here area some examples

“Which version of Greenplum Database software, am I running on the cluster?”
```
SELECT version();
```
Alternatively, the psql command utility can be used for the same, as following:
```
psql -d <database-name> -c "SELECT version();"
```

In both cases, the query result would be similar to

version
PostgreSQL 8.3.23 (Greenplum Database 5.7.0 build commit:f7c6eb5cc61b25a7ff9c5a657d6f903befbae013) on x86_64-pc-linux-gnu, compiled by GCC gcc (GCC) 6.2.0, 64-bit compiled on Mar 30 2018 14:19:06
(1 row)

“Which version of PostGIS extension, am I running on the Greenplum Database cluster?”
```
SELECT postgis_full_version();
```

version
POSTGIS=”2.1.5 r13152” GEOS=”3.4.2-CAPI-1.8.2 r3921” PROJ=”Rel. 4.8.0, 6 March 2012” GDAL=”GDAL 1.11.1, released 2014/09/24” LIBXML=”2.7.6” LIBJSON=”UNKNOWN” RASTER
(1 row)

“What is the population of the City of New York?”

SELECT
SUM(popn_total) AS population 
FROM
nyc_census_blocks;

population
8,175,032.00
(1 row)

“What is the population of the Bronx?”

SELECT
SUM(popn_total) AS population
FROM
nyc_census_blocks
WHERE
boroname = 'The Bronx';

population
1,385,108.00
(1 row)

“For each borough, what percentage of the population is white?”

SELECT
boroname,
100 * Sum(popn_white)/Sum(popn_total) AS white_pct
FROM
nyc_census_blocks
GROUP BY 
boroname;

</table> ## Next module [Geometry (PostGIS) SQL exercises](https://github.com/cantzakas/postgis-demo/blob/master/GEO-POSTGIS-SQL.md)